The Hogwarts Invasion
by CreativeWords
Summary: PotterWhoLock (but only lets me pick two) Something is threatening Hogwarts mere months after Voldemort's downfall. When it needs help, the Wizarding World calls on the Doctor, but will he be able to find the intruder before it kills again? And can student John Watson learn to move on after a fight for Hogwarts that claimed some of his dearest friends and nearly himself?
1. Prologue

**Author's Note:** This story is a Christmas present for a Potterwholockian friend of mine, but I'm having such fun I thought others might enjoy reading it, too. (If you're here from my profile, this is why I dropped my other stories for the last month. I love reviews and I own nothing but my own imagination. Thanks!

* * *

"Holmes."

Mycroft looked up, brow furrowed in irritation. He was no third year student, the time for surname-only titles was long past. The wizard in the grate didn't appear to notice his displeasure.

"Yes, Mr. Hotchfin?" he replied, stopping the furiously scribbling quill with the tiniest of flicks from his wand. "I'm quite busy. The Office for the Regulation and Control of Magical Creatures is expecting 20 copies of this report on Belgian dragon eggs by noon."

"It will wait. Shacklebolt wants you."

Mycroft rolled his wand between his fingers, the only visible sign he'd even heard Hotchfin. These were words he had been waiting four years to hear.

"Very well then," he said in a bored voice. "I'll just pop over, shall I?"

"He says I'm to bring you now and no fuss about it."

"Naturally. Well…" Mycroft appeared to consider. "Let me see if Anthea can take this project. Tell Shacklebolt I can be there in five minutes."

Hotchfin disappeared without so much as a nod of farewell. Mycroft allowed himself a slow grin of triumph. His years spent proving himself had borne exactly the fruit he hoped. Few would guess that the young wizard with the tiny office in a satellite branch of the Ministry had any power at all, much less that the head of nearly every Ministry of Magic department came to him in their hours of need. Barely 22, and a finger on the pulse of every major project in Wizarding government. And now Shacklebolt wanted to talk to him, only weeks after taking the top job. It really called for more than a grin, but time was short.

"Anthea," he called through the doorway.

The sharp taps of high heels informed him she was on her way several seconds before the tall witch came into sight. She gave the immediate impression of someone not to be taken seriously, from the sensuous way her brown hair was poufed and curled to fall just so on her cheeks, to the heavy, if pleasing, application of makeup, to the way she managed to make even the uniform robes seem somehow slinky. Mycroft approved of her most heartily. While she was no utter genius, she was reasonably clever and carried the added bonus of being the sort of person easily ignored. They were in an exclusive club – the Ministry's best weapons, perhaps even counting the Aurors. They shared the most desirable talent of forgetability, more useful even than invisibility. Few people remembered either of them. Even fewer could give a name to match to their faces. They moved from office to office, observing and reporting what they saw to those with power to do something about it. Men rose or fell based on the observations of these two who were huddled into the aging offices.

"You'll need to finish the Belgian egg report," he said, not bothering with a greeting. "It is to be submitted at the end of the hour. I've left the last of my notes on my desk. I have a meeting."

Anthea finished folding the paper airplane in her hand and sent it toward Accounting with a graceful wave of her wand. "Not Misuse of Magic again, is it?" she asked with a brilliant imitation of bored disinterest.

Mycroft shook his head. "Shacklebolt."

For a split second, Anthea's eyes gleamed with the intelligence she so carefully hid. Then she gave a vapid smile. "Well, then, hop to it, Mycroft Holmes. See if you can get us some nicer office chairs while you're there."

Mycroft took a handful of Floo powder from the jar on the mantel. "Quite right. I'll see what I can do."

He spared himself the usual ignoble entrance caused by Floo powder by a simple twist of his wand as the grate swung into focus, restoring his equilibrium. He was amazed at how many centuries of wizards had merely accepted this inconvenience without doing a thing to remedy it. His spell was under review by the Spell Approval Committee and could be published in spell books as early as next March.

"Mycroft Holmes." The deep, rich tones of Kingsley Shacklebolt greeted him as he stepped smartly through the grate.

"Minister," Mycroft replied, grasping his hand cordially. There was a definite aura of interest about the older man, but also a fine layer of skepticism. There had been talk about Mycroft's work under Pius Thicknesse in the last year, but his loyalty could not be called into question considering the hundreds of others who had compromised to stay in the puppet minister's good graces. And considering his efforts on behalf of the Muggleborns – well, Shacklebolt could distrust him all he liked, but he couldn't say Mycroft had done nothing.

It was difficult to tell what Shacklebolt was thinking as they walked back toward the desk. Mycroft was an excellent Legilimens, but there were certain persons on whom it was pointless to try it. Kingsley Shacklebolt was one such wizard. Mycroft would have to dispense with the easy way. It suited him just as well, as his own powers of observation needed little magical assistance.

Shacklebolt gestured toward the chair, the movement distracted at best. His pointing finger missed the chair entirely, indicating the floor space behind it. For a man as precise and efficient as the minister, this was a tell, and a disturbing one. Whatever they were to discuss, it was not the Belgian dragon eggs. Mycroft turned to the desk, noting the missives in neatly sorted piles. A glance revealed the common thread.

"Trouble at Hogwarts, sir?" he asked, seating himself, and turning to look at Shacklebolt, who still stood, facing the window.

Shacklebolt raised his eyebrows. "As fast as your superiors claim."

"Ah," Mycroft controlled the urge to sneer. "Am I to assume the pile of letters all bearing Minerva McGonagall's writing was nothing more than a test?"

"Of a sort," Kingsley said, the smile on his face not quite reaching his voice. "They do contain pertinent information, but I wanted to see the famous Holmes powers at work."

Mycroft was not a show-off like his younger brother, but he could respond to ego stroking as well as the next man. "Hardly a true test of my potential, I assure you, Minister. More challenging would be to say how I know your security detail has shrunk by two in the last week, your maiden aunt is either visiting or will be visiting shortly, and you wish to replace the atrium fountain before the new year."

Kingsley paced around and sat heavily in his own chair. "Impressive, Holmes."

Mycroft inclined his head at the compliment and waited.

"Minerva McGonagall is not a fearful woman," Shacklebolt began. "She may be getting on in years, but she's tough as boomslang skin and still a formidable duelist. So when she says she needs help because Hogwarts is not safe, you may be certain she means it."

Mycroft leaned forward, head tilted a few degrees left. "I would have thought, since May, we'd be done with all this."

"So would I. But Voldemort is by no means the only source of danger or evil in this world. Minerva has reported several unexplained deaths among the house elves. Bloody affairs. And even with Flitwick acting as Legilimens, no one can recall anything about it. Hagrid reports that his Thestral herd has been disturbed, and the centaurs have complained of attacks on their young. No deaths in either herd yet, but strange. It is a powerful being that will brave a centaur mother's anger. And odder still," Shacklebolt shuffled his papers till he found the one he wanted. "The security around Hogwarts has remained at the highest levels of which we are capable during the restoration this summer, yet none of the alarms or sensors have been triggered. Not in the kitchens when the killings happened, or in the grounds. Whatever is doing these things, they seem to be of non-magical origin."

Mycroft blinked at that, actually surprised. "Are you certain of this?" he asked quietly.

"No," Shacklebolt admitted baldly. "But I am increasingly aware that we have to consider the possibility."

It was an impressive admission from a man of his caliber. Mycroft adjusted his perception of him. Candor was a rare quality in the ministry, particularly candor that revealed weakness on the part of the speaker. For Shacklebolt, Minister of Magic, to admit a lack of knowledge to a man as far down the pecking order as Mycroft was a sign of both strength of character, and desperation. He leaned back, counting the newly-minted lines in the minister's face.

"But what do you need me for?" he asked at last. "You have the entire Auror office at your beck and call. You need only set a competent investigator to the task."

Shacklebolt grimaced. "The last thing this country needs now is a public reminder that dangers are still lurking. Anything sanctioned by my office is sure to leak to the Prophet within days. I am not the politician Thicknesse was," he said with a wry grin. "But I know when things must be kept quiet."

Mycroft gave a slight nod of understanding. This was language he knew and expected. "They are short a staff member, are they not?"

Shacklebolt nodded. Mycroft lifted his chin and steepled his fingers under it, narrowing his eyes in concentration. There was an idea, a solution that was gathering itself in the corners of his mind. A non-magical enemy would require non-magical help.

"I believe I have a candidate for the Defense Against the Dark Arts teacher," he said, meeting Shacklebolt's surprisingly patient eyes. "Minister, have you ever heard of the Doctor?"


	2. Chapter 1: On the train

Platform 9 ¾ was more crowded than it had been since he was a fourth year. John Watson edged past a Hufflepuff who seemed to be accompanied by his entire extended family and set his sights on a compartment that was, as yet, empty. The air around him was full of jubilant greetings and near-tearful farewells. Since May, the whole Wizarding community seemed to have given itself over to a holiday spirit that made them as free with their emotions as the average American teenager. John had entered into as best he could, but he had been at the castle that night, and it was difficult to marry wild elation with the remembrance of so many dead. Despite the festival atmosphere, he had seen a few faces that, like his own, were set to face the place that had haunted their nightmares of the summer.

"Watson!" The call halted him as he halted by the steps to a car that seemed least occupied.

"Lovejoy!" he called back, waving once as the blond girl made her way to him, pushing the trolley with trunk and ginger cat around another knot of boisterous family – this time crowded around a scrawny girl who could only be a first year.

There was an awkwardness that came with her. They had been close friends last year – both Muggleborns who had had their records altered by someone in the Ministry, both at Hogwarts illegally, and both determined to make as much trouble for Snape as possible. They had been in the thick of the fight together, back to back in the courtyard fending off monstrous spiders, giants and wizards alike. John's last memory of the battle was the billow of Lindsay Lovejoy's robe as she turned from helping him into the shelter of a pile of rubble and faced the oncoming Death Eater. There were shadowy memories of the Great Hall, the sunrise, the cheers that broke into the haze of pain and blood loss, then the face of Healer Gillysmythe in St. Mungo's three days later. Lindsay had sent a few owls, and he had replied with a good attempt at normalcy. But since then –

"When did you get out of St. Mungo's?" she asked, grinning in what looked like relief. "I was afraid you might not be able to come back for the start of term."

Her eyes had already found it. John swore in his head and shifted the cane so his jean leg hid most of it. The question on her face was obvious, and he had no intention of answering it.

"Got sent home three weeks ago. St. Mungo's was being extra careful with the under-17's that came in – didn't want to risk turning any more of us into martyrs."

Lindsay nodded, her eyes resolutely away from the object in John's hand. He leaned it against the inside of the train and held out his hand for her cat carrier. She hesitated, then allowed him to take it.

"I see Pippin made it through alright," he said, looking in at the ginger cat before climbing up a step and placing the carrier inside the train.

"Best I can tell, he was in the owlery the whole time."

Lindsay was eyeing the hand he held out for her trunk, but made no move to allow him to take it.

"Hand it over, then."

"Shoulder," she said pointedly.

"It's healed," he said in a tone of practiced easiness. "Half the summer in St. Mungo's can fix anything."

"I can get my trunk. You've got your own to manage."

The train whistled. John pursed his lips and hefted his trunk up the stairs. His left shoulder screamed in protest, but he fought through it and, with more brawn than finesse, threw it onto the luggage rack of the first compartment.

He hadn't fooled Lindsay, who had merely stepped behind him in the hallway with her own trunk and now put it next to his with a grunt that seemed nothing compared to what his had been. They returned to the corridor in silence to retrieve the cat carrier and his cane. She released Pippin and let him settle next to her on the bench. John sat across from her, the tension slowly building in his muscles. The compartment was too small, the air too warm, the corridor too loud. And across from him, a girl who knew too much. She was petting her cat with diplomacy, but he didn't like the fact she felt the need for diplomacy at all. They had been outlaws and fighters together last year, part of a group of Muggleborns who had been spared the purge and part of a much larger unit bound fiercely together by their desire to thwart Snape's regime. Now, with both those connections stripped away, and so much John wished to keep locked away –

The noise in the corridor really was too distracting. As the train sounded its final whistle and jolted forward, he heard the sounds of discord, voices raised in anger. Then, the unmistakable crack of flesh on flesh – a solid punch had landed. The tension coalesced – propelling John out of his seat and out the compartment door.

Wizarding robes and Muggle clothes were tangled around each other as the brawlers – two Slytherins and one skinny boy still in jeans went at one another. John grabbed the backs of the two nearest him – and the bigger of the two Slytherins and Jeans Boy. He twisted immediately out of John's grasp and raised his guard, focus only on the Slytherin still standing with fists raised.

"Calm down, the lot of you," John said, an edge of authority to his voice. It would have to be enough, as his wand was still in the compartment.

The lout John was holding kicked his right shin and his fingers involuntarily loosened. He attempted to regain his hold, but the lunged sent firebursts of pain through his shoulder. The boy turned and sent a rabbit punch at him. John ducked, bobbed to the side, and threw right hook of his own that the Slytherin caught on the chin. The boy stumbled, and John knew a flash of satisfaction at the surprise on his face at the power of the blow.

"Oi!"

It was Lindsay behind him, but now he'd attracted the attention of the other Slytherin. He settled into fighting stance, weight on the balls of his feet, and let his fists curl themselves up. The smaller of the two lunged forward and the big fellow went after Jeans Boy. John sidestepped just as the door to the car slid open and a Ravenclaw prefect entered the corridor followed by a man wearing a pinstripe suit. Jeans Boy got his chin clipped as he turned to see the newcomers and staggered back a step. The prefect, who John now recognized as Charles Boot, caught the boy as the man took charge of the Slytherin.

"Why am I not surprised?" Boot sighed. "Come along, detention for the lot of you. I'll inform Professor Slughorn."

The boy attempted to wrest his shoulder from Charles' grasp. Charles rolled his eyes. "Now, now, don't make me get Big Brother involved this early in the year. He's spoken with Professor Flitwick already. All the Ravenclaw prefects got instructions about you."

John peered curiously at the boy, but his face was averted, a near-silent stream of complaints streaming from his mouth. He didn't look familiar, but then John hadn't been close with many outside Gryffindor till the Carrows drove so many in the upper levels into hiding. This boy was too young to have been in that number.

"John, were you mixed up in this?" Charles' surprise was obvious.

"Jus t trying to break it up," Lindsay spoke up from the doorway.

Charles frowned. "I suppose I ought to talk to –"

"It's alright, Charles," the man in the suit said, drawing everyone's attention for the first time. "I'm sure our scrappers mean to behave the rest of the journey. Right boys?"

John found himself bristling at the intrusion. Yes, it was better than detention, perhaps, but who was this strange fellow and why did he have the power to dispense with a fair punishment?

"Right then, off with you," the man said, shooing them with his hands.

Jeans boy was the first to move, heading out the door Charles and the man had come from. The Slytherins made to follow, their faces still thunderous. John moved forward in protest just as the man blocked their way.

"Ah, ah," he said, crossing his arms. "I wasn't born yesterday, lads. Find yourself a compartment to that end of the train."

They turned around with only slight hesitation. John had to assume that even a Slytherin had more sense than to defy a man who was obviously faculty before the train was fairly out of London. The man watched them exit the car, then turned to the three remaining students.

"Thanks for your help, both of you," he said. " I'm the D – Professor John Smith, the new Defense Against the Dark Arts professor."

"John Watson."

"Lindsay Lovejoy."

There was a note of something in her voice that made John turn toward her. She was staring at John Smith as if trying to place where she'd seen him before, or trying to decide if he was familiar or not.

"Well, then, we'll be off. Have a good trip – no more fighting, mind," he said with a grin. "Now, Charles, what's next on the tour? Fascinating way to travel…"

Charles was full flow into the origins of the Hogwarts Express by the time the door closed behind them.

"Did he say, 'the tour'?" Lindsay asked as they reentered the compartment. "Like he's never been on here before?"

John, whose shoulder and leg were both setting up quite the protest, eased himself onto the bench with a careful shrug. "Went to another school, maybe? Beauxbatons or the American one or some such?"

"Could be," Lindsay said, reaching down for Pippin. "But he sounds like he's from here."

"Sounds as if we'll find out more tonight at the feast."

Lindsay looked slightly disappointed but accepted the subtle shutdown. John had no desire for conversation just then, particularly not speculation about something they would find out in a few hours, by which time his limbs would have ceased throbbing. He leaned his head back and let his mind travel to Hogwarts. Would it be completely repaired, all signs of the previous year erased? Would he prefer it that way, or with a few scars still visible? His eyes slid closed and he saw the courtyard alight with a dozen jets of light, stone pillars tumbled from their places, combatants falling left, right and center.

He jerked his eyes open. He would not dream about it - not here, as the hatefully clacking wheels took him ever closer to the physical location and the girl who had fought alongside him sat there in suffocating normalcy.

Healer Gillysmythe had suggested he speak to Madam Pomfrey or a professor he trusted upon his arrive at school, to set up some sort of therapy or counseling to deal with these recurring dreams that no spell or potion could diminish. He knew full well that he would not go. He was a Muggleborn, he had an innate understanding that magic was not the answer to every problem.

Whatever this demon was, the key to fighting it did not lie at Hogwarts.


	3. Chapter 2: The Unfamiliar Familiar

It was odd, John thought, seeing Minerva McGonagall in the throne-like headmaster's chair. Not sickening, as it had felt when Snape sat there, but an odd reminder that returning to school did not mean a return to how things were. She was a thin woman, but the chair did not dwarf her. She sat ramrod-straight and proud, claiming the new position with her natural dignity.

"She looks upset," Lindsay observed quietly from across the table.

There was a tiny knot of survivors from the battle who had congregated at the far end of the Gryffindor table. Ginny Weasley and Hermione Granger were not among them, having been immediately swept to the head of the table, where both looked fairly uncomfortable, surrounded by adoring eyes. After the initial boisterous greetings, the group had tucked into the meal and a sort of communal discomfort that, while not overpowering, was definitely at odds with the rest of the hall. Lindsay seemed to be the closest to be pulling out of it, but even her trademark gusto was more contained, her gaze sharper than John recalled. He turned back to look at McGonagall.

"It's her first start-of-term speech," he observed.

"Maybe that's it." Lindsay was unconvinced. She cut her eyes down the staff table next to Slughorn, where the new teacher sat chatting with Sinistra on his left. "I still say there's something different about that new professor."

"The job's jinxed," said Dean Thomas, who had been on the run most of last year and had been one of the few who decided to come back and complete his seventh year. "When was the last time someone stayed longer than a year? Even with You-Know-Who gone, I reckon it's not an easy post to fill."

"Voldemort," John said suddenly, and rather louder than planned. Most of the people around him jumped. A few head swiveled round, but he didn't care. "He's good and dead, isn't he? Why not use the bloody name?"

It might not have been so awful if Professor McGonagall hadn't just risen from her seat, prompting the noise to die down around the room. Curious eyes now came from other tables, and about half the staff had turned their attention from McGonagall to him, including the new teacher. Lindsay held out a bowl of pudding with something like amused understanding. John accepted it with poor grace, attacking the gateau with ferocity.

"Good evening, students," McGonagall began, her clipped Scottish butt somewhat sharper than usual. "Welcome to a new year at Hogwarts. Whether you were a part of the events of last year or have never set foot in this castle till tonight, the staff and I are thrilled to see you and offer you a year of learning without the pall of war hanging over us."

Lindsay was right, John decided. McGonagall looked uneasy, and he didn't think it was just nerves. Her eyes flickered often over the students' heads, searching the corners, the windows, the doors. John tuned out her words, following the path of her eyes. Nothing seemed out of place. The room was brighter than it had been last year, making it harder for anything to lurk in the near-nonexistent shadows. He looked up at the ceiling. It was partly cloudy, the last rays of sun catching the fluffy edges. He wondered, not for the first time, if anything could hide beyond the enchanted barrier, or if the mirage of sky pressed against the rafters. His 11-year-old Muggleborn fascination had turned to watchfulness last year, when spies and dangers were everywhere in the castle. Still, he'd never seen any evidence that something could hide there, and McGonagall didn't seem to be paying it any more attention than the rest of the room. He turned his attention to the ornamental tapestries lining the walls.

"… am pleased to introduce the newest member of our faculty, Professor John Smith."

John started clapping automatically when others did, but it wasn't until he saw the man in the pinstripe suit stand that his mind left possible hiding places in the room and returned to Professor McGongall's speech.

"Professor Smith will be teaching Defense Against the Dark Arts this year." Another spatter of polite applause. 'He is new to the castle, having been educated elsewhere, so I trust you will all do your best to make Hogwarts feel like home."

Did John imagine it, or had she hesitated before saying "elsewhere"? Why the vagueness? Why mention it at all? He caught Lindsay's eye and saw the lingering suspicion there as well.

_Paranoid_, he told himself ruefully. Too used to looking over his shoulder to find trouble. Healer Gillysmythe had said the same. There was no trouble to be had here. Hogwarts was safe. He'd helped make it so. Then why did his stomach feel heavier than it had while watching for the Death Eaters to descend upon them?

He was one of the last ones out of the hall by choice. He had no desire to be bowled over by the first years and his leg wasn't up to sprinting to beat them. He wasn't looking forward to tackling the seven flights of stairs, either, and preferred to do it without a hundred pairs of eyes to watch. It was with a silent groan, therefore, that he saw Lindsay Lovejoy waiting with an indecisive air at the base of the stairs, having just waved the last group of students past her.

"I wasn't sure if you were coming or –"

"Or decided to sleep in the Great Hall?" John asked, the joke coming out far harsher than intended. Her reflexive smile looked anxious at the edges. "I think Mr. Filch would be only too happy to slap me with detention for that."

They both chuckled. John wondered if her laugh was as forced as his. They took the first few steps in unison.

"So," said Lindsay, visibly slowing her pace to match the tap of the cane. "Professor Smith is our head of house this year. That will be a change."

John paused at the first landing. "What?"

"Just now, in the Great Hall," Lindsay prompted. "Professor McGonagall said she would keep the Transfiguration courses until a suitable substitute could be found, but she's giving the duties of head of house to Professor Smith." They took the next flight slower still. "I thought it was odd, since he can't be a Gryffindor proper if he went to a different school. But I suppose most of the teachers are Ravenclaw or Hufflepuff and aren't qualified either. I wonder if there are any other Gryffindor professors now?"

"Hagrid," John offered, a real laugh in his voice this time.

Her eyes lit up. "Yes! That would be fantastic!"

It was almost like last year as they took the remaining flights – flashes of camaraderie as they staved off the moment to moment uncertainty with jokes. It lasted all the way to the portrait hole, where a Ravenclaw girl was saying a rather passionate goodnight to a Gryffindor boy. They gave no indication that they'd noticed the newcomers.

After about 30 seconds, John gave a loud _harrumph_ which split them apart as effectively as a Repelling charm. The Fat Lady gave a sigh of relief that made Lindsay laugh as the couple exchanged a parting kiss and the girl turned down the corridor toward the Ravenclaw dormitory.

"Gillywater," the boy said dazedly, and the Fat Lady swung open to admit them.

"I suggest you drink some and cool off," she said as he passed, turning a friendlier eye on John and Lindsay. "I was getting claustrophobic with them pressed up against my frame like that, and you know I _couldn't _leave till everyone is inside for the night. I don't care if they haven't seen each other since May, it's just good manners to do such things in private." She eyed them with sudden severity. "I hope you two weren't planning –"

"No, we're just –"

"Of course not!"

The indignant exclamations came from both of them simultaneously, not defensively, but with the amused surprise of friends. The Fat Lady looked unconvinced, but John knew by the gleam of pure merriment in Lindsay's eye that the denial had been expected and welcome. People always assumed he was "with" any girl within hailing distance. He'd never understood it. He'd had his share of girlfriends, it was no good denying it, but he had no aspirations to conquests or gaining a reputation.

He climbed through the portrait hole, swinging the cane through first, and nearly smacked into the back of Professor Smith. He sidestepped just in time to allow Lindsay the honor.

Lindsay rocked back immediately, and Smith stumbled forward a step, breaking off midword as he threw out his hands to right himself. He turned around to face the two students, both of whom were pink with embarrassment.

"Well, then," Smith said cheerily. "You must be the last two. I've just come up to get properly introduced to everyone in my house. Class lists aren't much help if you don't know the faces, are they? But then, I've already met you, haven't I?"

John nodded shortly, doing his best to ignore the laughter floating around the edges of the common room. He shifted his cane behind a fold of his robes, but had no doubt a good many had seen it, including the professor, considering the way he was looking at him as they shook hands for the second time that day. The man was younger than he'd seemed either on the train or in the Great Hall, but he had a weariness in his eyes that John recognized, and the realization surprised him. It was the weariness that had settled in John at the first disappearance last year – the acceptance that battling on, while the only right choice, would be a costly thing indeed.

He shook himself into the pleasant expression that had become his armor as Professor Smith turned to Lindsay.

"So," Lindsay began, only tinged with pink over their unceremonious introduction. "You're to be teaching Defense Against the Dark Arts this year?"

"That's right," he said with a breezy confidence. "Should be a good year."

"Ever taught the subject before?"

So, Lindsay had picked up on the too-casual note as well. Having seen the man up close again, John was no longer so eager to brush off concerns about him. Something didn't add up, and that was certain.

_Paranoid._ He mocked himself.

Professor Smith's smile had slipped a notch. "Not exactly, no," he said, fumbling inside his coat pocket for a piece of paper. "But I've got loads of teaching experience, see?"

Lindsay looked down at the paper, blinked, and looked again. Her eyes when she returned them to Professor Smith's were skeptical. "Do you habitually carry a list of your teaching posts with you?"

Smith folded the paper with another wide smile. "Not habitually, no." He turned to face the room, now humming with conversation. "Good night to you all. Should you need me, I've taken the Defense Against the Dark Arts study rather than Professor McGonagall's old one, so come look for me there. You'd best get to bed soon. Tomorrow will be an interesting day."


	4. Chapter 3: Mr Sherlock Holmes

John had reason to agree with the new professor before the day had fairly begun. He'd woken his dormmates around midnight, yelling at the giants laying waste to the courtyard in his dreams. They'd all been awkwardly nonchalant about it, merely crawling back into their own beds once it was clear he was not having some sort of fit. He, on the other hand, had been too ashamed to sleep after that, so lay utterly still for the remaining hours of night, letting the rhythmic snores in the room mark the passage of time.

He leaned on his cane more than usual when, as the first rays of dawn hit the tower room, he dressed and headed to the Great Hall. Professors Vector, Sinistra, and McGonagall, and two Hufflepuffs were the only ones there as he sank onto the Gryffindor bench and let his head rest on his folded arms. The quiet refuge lasted only a few moments.

"Watson." It was McGonagall's voice side him.

He jolted into an upright position, spine cracking with the sudden motion. "Yes, Professor?"

She gave him an appraising look and held up a letter. "Your parents wrote me about you. Said they're concerned about you returning to school so soon."

"I've had the same time as everyone else," John said, trying to keep his voice as pleasant as the expression he'd pasted carefully onto his face. "My parents worry too much."

"In this case, it sounds as if they have good reason, Watson. That curse could easily have killed you. Your parents say the healers at St. Mungo's only released you at your own insistence."

"It grazed me." There was no keeping the snap out of his voice. John took a breath and continued, voice as clipped as McGonagall's. "The healers did all they could. No reason to stay there when I could take my potions at home."

He regretted mentioning that when McGonagall shifted the pages of his mother's rose stationery and held out a prescription. "Yes, your mother said you left this. You're to take it to Madam Pomfrey today to have it filled." Her eyes flickered to the cane resting beside him. "As you have time, of course."

John took the paper, fighting mightily the urge to rip it into shreds. Professor McGonagall must have seen.

"I'll be sure to let Poppy know to expect you."

"Thank you, Professor," John said heavily, choosing to stuff the paper into his pocket instead. He derived some small satisfaction from the way it crumpled against his fingers.

McGonagall started to walk away, but turned back, seeming to weigh her words before she spoke. "Thank you, Watson."

He blinked up at her, brow furrowed. She folded the letter, replaced it in her robes, and put her hands behind her back.

"You won't get the accolades that some of your classmates will, Watson, but some of us saw. You did your house proud last year."

Minerva McGonagall was not one for long speeches. This, John knew, was tantamount to getting an Order of Merlin. He was saved the embarrassment of coming up with a reply by a knot of students coming in the door. With relief, he saw that Ginny Weasley and Hermione Granger were among them. There would be no spare glances for him with these two living legends in the room.

McGonagall glanced back at him as she swept down the table. "I'll give this to Professor Smith, since he's your head of house now, Watson."

He wanted to shout after her that it wasn't necessary, that the stranger had no need to read his parents' message, but the Great Hall was quickly filling up and he had no desire to make another scene. He turned his attention instead to the food in front of him, slathering a piece of toast with strawberry jam. If he was going to have to face Madam Pomfrey, he wanted sustenance first.

Professor Smith came by with class schedules. John took his without looking up. Charms, Defense Against the Dark Arts, Herbology, Potions and Transfiguration. All the classes needed to pursue a career as an Auror. Or a healer. He'd never quite been able to make up his mind between the two. Him mum always said his problem was that he had a hero complex _and_ a helper's instincts. A passing first year bumped into the bench near where he sat, sending his cane clattering to the floor. John stared at it, wondering if this was some sort of heavy-handed message from fate. Not a chance of him being accepted into the Auror program now.

He was jolted from his morbid glare by Lindsay seating herself to his left.

"Transfiguration first thing for you, too?" she asked, munching on a slice of bacon from the tray.

He looked down at the schedule. "Uh – yeah, then a free period, then Defense Against the Dark Arts. There's something to look forward to."

Lindsay threw a glance at the staff table. Smith was talking to McGonagall, his face serious. "Funny thing," she said, turning back to John. "For a second, when he showed me the paper last night, I could have sworn it was blank. But I blinked again, and it was all there like he said."

"Sounds like a Zonko's gag parchment."

Lindsay nodded. "That's what I thought, but why bother? It was barely noticeable. And not really something I expect from a Hogwarts teacher."

"Yes, well, you also didn't expect that one bloke to be a werewolf."

He'd said the words with an edge, trying to shut down the conversation, but she grinned so broadly that he let out a laugh. It was a rough bark of a sound, unfamiliar in his own ears, but somehow comforting to know it could still call itself into action.

Lindsay snagged another piece of bacon and swung off the bench. "C'mon, I bet 'Headmistress McGonagall' is even more of a stickler for punctuality than 'Professor.'"

A period of Transfiguration left his head spinning and his leg even less willing to navigate the stairs, but he resolutely left the queue of Gryffindors headed back to the common room and headed to the hospital wing, hoping to catch Madam Pomfrey at a time when most students would be occupied elsewhere.

She answered his knock with a smile. "And I thought I would have to track you down. Stoic John Watson, the healer with no time for himself."

It was comforting to be back here. He'd been the underground supplier of healing potions and salves to the students the Carrows got their claws into, spending the first month of school sneaking into the hospital wing with various excuses and raiding the cupboards when Madam Pomfrey was occupied. She had become an invaluable ally when she caught him searching the shelves for a burn salve, dripping blood from a cut on his cheek where Amycus had punched him with a ringed hand for interfering with the barbarous punishment. Somewhere between her fixing up his face and his confession of being the one who had been raiding her stores, they'd reached an agreement to help each other.

He held out the crumpled prescription sheepishly and took the chair she indicated. "These are just in case I need them. Not a regular dosage."

"Healer Gillysmythe is no fool," she said. "If he says you need these, you do, and none of your Gryffindor heroics here, young man."

"Guess the time for that's past, isn't it?" he said, face twitching into what he hoped was his armor-plated smile.

Madam Pomfrey turned from searching the tall cabinet. "At least the kind that end up with children fighting an adult's war," she said gently.

He didn't miss the relief on her face, and because he understood her thought, he nodded. She put the vials down in front of him, and he ran his eyes along the labels, though he knew them by heart. The soothing yellow paste to be applied to his shoulder and leg, Dreamless Sleep for the nights he was too tired to face the nightmares, and his particular un-favorite, the Draught of Peace. The healer's well-meaning attempt to medicate his mind did no good, and did not ever expect it to.

"Thanks, Madam Pomfrey," he said, grabbing the vials and standing.

"You know," she said, with a fine attempt at subtlety. "I can always use some help up here. If you want to come and help sort potions and… talk, maybe? About what happens to you, and such."

So Professor McGonagall had shared the entire message. John looked at her wearily and didn't bother pretending any longer. "Nothing happens to me.

Her worried face stayed with him as he hobbled to the Defense Against the Dark Arts classroom just in time to join the end of the queue as they filed into the room. It had been purged of the awful pictures and general dim grisliness of last year and felt rather as it had their first year when Gilderoy Lockhart's tooth-grinding enthusiasm had set the tone. He stumped to a seat in the middle of the classroom and slung his bookbag to the floor.

"Watson!" It was Robert Cadwallader, a Hufflepuff who had helped organize Dumbledore's Army last year. He raised his hand in a smart salute that made John's stomach lurch unexpectedly.

Robert sported an impressive scar on his right cheek, but looked otherwise hale and hearty. "It's good to be back isn't it?

"I'll let you know at the end of the day," John said. "One class with McGonagall and I feel like a first year who skived off lessons the day we were taught 'swish and flick.'"

"It'll come back easily enough," Robert laughed. "I saw you that night – dragging kids out of that collapsed wall section, shooting jinxes at every Death Eater in spitting distance. Thought you'd go till they knocked the castle down around you. What happened after we got separated?"

John shifted his cane, suddenly, unreasonably impatient. "I guess you could say I got knocked down."

The smile faded inch by inch. Robert cleared his throat. "Well, good to see you back. I'd better find my seat. New professor's here."

John sank into his chair, willing the boiling resentment back down to a slow simmer. He remembered Robert helping him with the frightened fourth and fifth years who'd tried to sneak back after his group had gotten past Filch. That wall falling had been a moment of utter clarity, shouting orders to those who had clustered to lend a hand.

He was pulled back into the present as Professor Smith swept past him to the front of the classroom. Despite the teacher's solemn black robes and impressive pile of books, Smith looked displaced, somehow. Maybe it was the hair – jutting up all over his head, or the red Converse shoes he'd never seen on Wizarding feet, or the way the man's eyes roamed the walls, looking over the students' heads rather than at them. Whatever that parchment he'd shown Lindsay said, Smith looked nervous.

"Well," he said finally. "This year. A brand new year, isn't it?" He strode a few paces to his right. "A fresh start, in a way. And I think it's time our Defense Against the Dark Arts curriculum got a fresh start, too."

John snorted along with a brave contingent of the class, neverminding the professor's confused frown. With any luck, Smith would be the sort of professor who routinely forgot homework assignments. He reached carefully into his book bag and pulled out the parchment with his Transfiguration homework. _Review the spells listed in chapter 1 and be prepared to perform them next class. Research the origins of interspecies transfiguration and prepare a –_

He was suddenly aware that Smith had stopped speaking. He cut his eyes over to the professor, laying the parchment on the empty other half of his desk. The man was flicking his wand rather desperately at the blackboard. Another titter ran around the room.

"Sorry," he said, shaking his wand arm as if to release tension. "It's just – new wand. Unwieldy thing, you know." He laughed, but most of the students did not.

"Would you like some help, Professor?" Only Hermione Granger could ask the question without sounding snide. John almost rolled his eyes.

"No, thank you, Miss… Granger," Smith said, taking a moment to recall her name and locate her in the front row. He took careful aim and sent a precise flick at the blackboard. Words appeared this time.

_7__th__ Year Defense Against the Dark Arts Objectives_

_-To accurately identify and defend against dark creatures_

_-To achieve proficiency in nonverbal defensive magic_

- _To learn protective measures that render the previous objectives nearly useless_

John caught Lindsay's eyebrow raise and grin from three desks over. The room was slowing filling with whispering as the students got to the end. If he thought he would keep this particular group of Hogwarts students from flexing their dueling skills, he would be sadly surprised.

"Lest you fear this will cut out your all-important dueling time, I assure you that all the objectives listed on the board will be covered," Professor Smith said, twirling his wand idly in his right hand. The sentence was greeted by a muted cheer. "But I want to remind you that the main purpose of this course is to train you how to keep yourselves and those around you safe."

From the spinning wand, a spark of blue light flew into the air, expanding and reforming instantly into a thundercloud that glowed with a great internal bolt of lightning before releasing a deluge across the classroom.

Smith let out an exclamation and pointed his wand at the cloud, his eyes so wide they seemed to take up half his face. The rain only pelted down harder. Several wands pointed to the ceiling, but an unfamiliar male voice was the first to ring out.

"Meteorolojinx recanto."

The cloud dissipated and the room filled with the mutterings of students drying themselves off. John did the same, reaching with a feeling of dread for the parchment with his Transfiguration assignment. The letters had run together beyond hope of recovery. He squinted at it rather desperately. Had it been 4 or 6 feet of parchment on the interspecies transfiguration essay?

Smith had pinpointed the source of the spell. "Ah, Mr. Holmes, thank you. Class, some of you may know Mr. Sherlock Holmes. He's a fifth year, but due to some very impressive exam scores submitted this summer, he's being allowed to take NEWT level courses."

The class turned as one to face the boy on the back row, who returned their gazes with an air of supreme disinterest. John squinted carefully, an incredulous smirk growing on his own face. Yes, the floppy-haired boy was the one he'd helped on the train. He'd seemed even younger when dodging the Slytherin's fists, but it was still quite apparent he was in the wrong class. The other students seemed to agree, based on the low rumble of chatter. John personally didn't care one way or the other – let the lad have a taste of NEWT level homework and he'd likely be begging for his regular fifth year load.

Smith was attempting to regain the students' attention. "So," he said loudly. "One thing I want to introduce immediately is a term-long project. You will be divided into pairs and complete the majority of your homework assignments in teams. Your final grades will reflect not only how well the assignments are done, but the amount of teamwork involved in completing them."

The man really was determined to turn every student against him in one class period, wasn't he? John could see the majority of the Ravenclaws, including Sherlock Holmes, looking positively outraged. Hermione Granger looked slightly ill.

"These assignments will range from research to physical dueling drills, so remember that the library lovers in the class will not necessarily be carrying all the weight. You should bear that in mind when choosing a partner – which you'll be doing right now."

There was a flurry of activity as students stood to locate friends at the desks around them. John cast a glance over at Lindsday, who shrugged her agreement. He'd just turned to reach for his cane when Smith whistled shrilly, halting everyone in their tracks.

"One last thing, though. I don't want you to choose a partner from within your own house. In fact, the less contact you've had with the person the better. Now – allons-y, all of you. I'll give you two minutes to get paired off."

The resultant explosion of sound was the biggest yet. Ginny, Luna and Hermione had queues forming around them, as did a few of the better known members of Dumbledore's Army from the previous year. John took a step toward Robert, but a Slytherin girl had just marched up to him and seemed to be demanding to be his partner. She'd have a rude awakening when she found out that Robert, for all his friendly loyalty, had missed out on the Hufflepuff characteristic of hard work.

He turned on his heel, heading toward the back of the classroom. A Hufflepuff girl was chatting with Lindsay, fingers twisting her chestnut ponytail nervously. John thought he'd seen her at a few DA meetings, but she hadn't made much of an impression. Smith was already beginning to make a circuit of the room, jotting down partner names. A heavy feeling of dread settled in John's chest as he took a few more steps up the aisle. He was going to get stuck with some Slytherin troll, it was inevitable.

One step more, and his eye caught perhaps the only other person still without a partner. Sherlock Holmes. Still leaning back in his seat, eyes darting about, but the rest of his body totally relaxed, he was the picture of disinterest, complete with a scornful look that hinted that even these older students were beneath his notice. John sighed. Not a Slytherin troll, but a Ravenclaw snob was just about the same cross to bear. Still, there seemed to be little alternative.

The boy saw him walking toward him and acknowledged him with an eyebrow raise, but made no move to meet him, despite the fact that John was leaning more heavily on his cane than usual. John gritted his teeth and walked the remaining few paces to the desk.

"John Watson," he said, sticking out his hand. "I don't believe we've met."

"Sherlock Holmes, and no, we haven't." Sherlock took his hand briefly, giving it a millisecond of contact, then releasing it.

"Well then," John said as the seconds ticked by and the noise in the room began to subside. "Fancy partnering for this? I don't seem to have a lot of prospects."

Sherlock started as if from a daydream. "Oh, I thought that was settled."

"Settled? Settled how?" John asked, patience wearing thin with the wunderkind.

"You came over here, introduced yourself, I reciprocated, and we shook hands. This entire sequence never would have happened if you hadn't been looking for someone to pair up with. I, obviously, don't have another partner, and you're still standing here. Only conclusion – we'll be doing Defense Against the Dark Arts homework together this year. By the way, courtyard or castle?"

"What?"

"For the battle," he said impatiently. "Were you inside the castle proper or out in the grounds?"

John stared at him. They'd never met, and this boy certainly hadn't been present at the battle. How, then, did he…

"Alright, then, boys – decided to team up?" Professor Smith asked, stepping up with parchment in hand.

John glanced at Sherlock, who was looking with sudden intensity out one of the windows. Not a promising start, but they were both short on options. He nodded.

"Looks like it."

Professor Smith twirled his quill and put it to the parchment."Got it. Sherlock Holmes and John Watson.


	5. Chapter 4: The House Elf

Sherlock, it turned out, was also in NEWT level Charms, Herbology, Potions, and according to the whispering students at lunch, Arithmancy and Ancient Runes. The only professors who refused his application were Binns and McGonagall, and he hadn't applied for NEWT courses in Care of Magical Creatures, Divination, or Astronomy.

John, on the other hand, had spent the day trying to figure out why the name Holmes had a familiar ring to it. He was eating treacle tart at dinner before Lindsay finally supplied the missing link.

"The Obliviator who modified my memories for the pureblood program mentioned that a Holmes had rearranged his work schedule so he could do that session."

"That's it!" John snapped his fingers. "The letter my parents received in June – it was from the office of a Holmes. Only time I saw the name, but then I read that letter about 50 times before we came back to school."

"So, this kid's father?" Lindsay speculated.

"I suppose I could ask him this evening," John said. "We're meeting in the library after this to begin that lethifold assignment for Smith. How about you and your partner?"

"We're taking different aspects of the lethifold to research and will meet up tomorrow sometime for a progress report. She seems fairly excited about the project – nice thing about having a Hufflepuff for a partner."

"Lucky. I've got the child genius who couldn't even be bothered to say that he'd agreed to be my partner," John groaned, pushing the plate back and rising from the bench. "If he brings my grade down because he's too brilliant to do the work, I'll hex him so he won't remember where the Defense Against the Dark Arts classroom is."

"No, you won't," Lindsay replied matter-of-factly.

They made their way out of the Great Hall and into the entrance. John glanced down the corridor toward the library with a heavy sigh.

"Don't suppose you have any particular need to go to the library?" he asked, half-joking.

"All my books are upstairs, and I want to get a head start on that Transfiguration assignment. But hey, if you get back soon enough we can practice those spells together."

John groaned. "All I want to do is get to bed and try and let my brain recuperate from this day. But yes, I'll probably look for you when I get back."

Lindsay grimaced her understanding and turned toward the stairs. John waved a hand and walked on toward the library. Even though it was nearly empty, it took him a while to find Sherlock, at one of the back study tables, so deeply engrossed in a book that John had to risk Madam Pince's wrath just to get his attention.

"Oh, yes, John Watson," Sherlock said, closing the book suddenly. "Lethifolds."

John sat across from him, cursing himself for feeling like he was the one who was awaiting instruction. "I was thinking we could both take half of the research. Maybe get an outline together tonight so we know what we're both doing. We don't know yet how this Smith fellow marks his assignments yet, but I'd imagine better safe than sorry."

"More on the level of Binns than McGonagall," Sherlock said with a dismissive shrug. "He'll give out E's for P level work just because he's trying this heavy-handed experiment to make everyone believe that working together somehow makes us all safer at night."

A memory of Lavender Brown as he had found her body – alone and bloody in the corner of the courtyard – sprang into John's mind. "Not a bad lesson to teach," he said stiffly. "You wouldn't know much about that, I expect."

Sherlock cocked his head at him, half-smiling. "When we met this afternoon, I asked 'courtyard or castle', and you seemed surprised."

"Well, a bit, but not now," John clarified. "You probably saw me last year or read my name in the Prophet over the summer or someone said something to you. However it happened, you're not some sort of seer whose clairvoyance will keep him protected always."

"Agreed," Sherlock said, leaning forward on the table. "But seeing things can go a long way toward keeping me safe. For example, I know you're a Muggleborn, with a sibling, probably younger, who is not magical. I know you fought in the battle of Hogwarts in May and were probably one of the instigators of the little rebellions going on last year. You _were_ injured, but your limp is at least partly psychosomatic. You also don't trust Professor Smith or, incidentally, me."

"How?" John wished he hadn't let the word out.

"Muggleborn – when you came up to me today, you shook my hand right off. That's distinctly a Muggle greeting. Wizarding families do, naturally, but we're old-fashioned. We like the bow, the curtsy, the doffed hat – then the handshake. You didn't even start with a nod, just straight off stuck out a hand. When you did, I saw your tan line – slight browning on the hand, none past the base of your thumb. Muggle clothes doesn't have sleeves that come down that far, and the sunstreaks in your hair tell me you're in sunlight as much as you can be. So, wearing a long-sleeved garment most of the summer and not brown enough to have been on holiday with wizard friends. St. Mungo's, obviously, given the cane and the way you hold your shoulder. And speaking of the cane – your limp is very pronounced when you walk, particularly when you're unsure, as when you were walking up to me in the classroom earlier today – but you stood talking to me for several minutes without leaning on it more than a few moments, which means the root is psychosomatic."

He gestured to John's book bag on the table. "There's a quill sticking out of your bag, obviously one that you use frequently. It's not the sort you would buy at Scrivenshaft's, it's the kind that Muggles sell in bookstores for calligraphers. Not as high a quality as something you could get for a few Sickles in Diagon Alley – but you use it daily. A gift, then, from someone close to you. Family. Parents would have given you something nicer, even if it was Muggle-made. Someone who doesn't have a large cash flow yet. Sibling. Could be a friend, I grant you, but brother or sister is more likely, since you don't seem the type to have told your Muggle friends about your powers. Based on the nib metal, I'd say younger sister."

"As to the distrust: well, your face betrays you. Human beings have a finite number of facial expressions and certain among them are universal. When I see a man with eyes as narrow as yours and chin tilted up and to the side, I can only assume he expects to be lied to. I saw it when you were listening to Professor Smith, and you're making it right now – though not so strongly as before," he added, seeming interested.

"And the rebellion last year?" John heard himself ask, still about three links back in the chain of reasoning, but finding each one rang true.

"Ah, technically more of a guess, I admit, but a solid one. You are a Muggleborn who was at the battle. There were precious few of those to begin with, and even fewer who saw much action. You saw enough to get fairly seriously injured, but didn't get yourself killed in a battle of fully-qualified wizards and all manner of monsters. For you to have done both means you were ready and waiting for it. The group calling themselves Dumbledore's Army reformed last year and made no secret of the fact they were preparing to make a go of it whether Harry Potter ever came back or not. And I saw on the train that your method of breaking up a fight is to end it yourself. Obviously not afraid of a fight."

He leaned back and spread his hands. "Did I get anything wrong?"

John blinked. "No wonder you didn't bother with Divination," he said at last. "That was amazing."

"All of it? Well, that's a surprise. There's usually something," Sherlock said, smirk slipping into a real smile.

"The quill is from my aunt," John said. "She gave it to me while I was in St. Mungo's."

"Aunt! Of course, less knowledge than a sibling, just picked based on look," Sherlock muttered. "See? Always something."

"Well," John was slowly regaining his equilibrium. "You did leave out my rank in Dumbledore's Army, but I suppose I can forgive that."

Sherlock leaned back and studied him. "Second or third in command, I'd say. Not the leader. You have the presence and authority, but you waited until I'd confirmed I would be your partner before you acted. Not general, at least not yet."

John was still scrambling for words when a scream from the hallway stopped the words in his throat. Sherlock leapt to his feet and was halfway out of the library before John could grab his cane. They raced along the stacks of books, skidded past a confused Madame Pince, who was peering into the corridor, and ignored her remonstrances as they pounded through the entrance hall to the corridor that led to the kitchens and the Hufflepuff dormitory. The chestnut-haired girl John had seen with Lindsay was standing, hand over her mouth, staring at the floor. John and Sherlock halted, and John's cane skidded on the floor as he came to full stop. He realized with a lurch that he had placed it in a pool of blood.

It was a grisly sight, even for him, and he'd held Michael Corner's head as he gasped his last from an Entrail-Expelling Curse. A house elf lay mangled on the floor, torso nearly missing. A few tendons and scraps of skin stretched over the space that should have been a tiny body. The neck had been snapped, and there were claw marks on the skull and shoulder.

The girl half-collapsed against John, who let her bury her head on his shoulder. He wanted to look away, too, but the sight drew him like a magnet. Sherlock had lowered himself so he was almost prostrate on the ground and was examining the claw marks mere centimeters from the dead elf's staring, tennis ball-sized eyes. He flicked his wand and a vial appeared by his side. His wand prodded the torn edges of flesh and deposited a sample of bloody fluid from the spot where the neck savagely ended. Something caught his attention at the wound, and he bent even closer, a feverish light in his eyes. He whirled around and faced the girl.

"You. Did you see anything?" he asked, bounding to his feet in a vampirically swift motion. "An animal? Person? Shadow? Anything? Answer me!"

"Sherlock!" John snapped as the girl trembled against him. "Give her a moment. This is a shock."

"It's not as if she knew it," Sherlock countered dismissively. "It's not a person."

"His name was Chimmy. He cleans the Hufflepuff common room on Tuesdays and Sundays and he likes to leave leftovers in this corridor as a treat for Mrs. Norris." The girl's voice was shaky, but she'd lifted her head and was staring at Sherlock with a fragile sort of dignity. "He was born here and he's technically a free el-"

"If you can recite the elf's entire life story you can answer my question," Sherlock interrupted. "Did you see anything? Anything at all?"

She'd just begun to shake her head when a cohort of staff members rounded the corner – McGonagall, Sprout, Flitwick, Vector and Smith, followed by Mr. Filch wheezing, Mrs. Norris at his heels. The cat's yowl of surprise made the girl shudder. John kept his arm firmly around her shoulders.

""Explain yourselves," McGongall spluttered, staring at the carcass and the three teenagers who stood clustered around it.

"We heard the scream," John volunteered, realizing with a start that barely more than a minute could have passed since they arrived. He glanced at Sherlock, who was slipping the vial into his robes, and continued. "It was already like this when we arrived."

"Molly!" Professor Sprout exclaimed, taking the girl from John's grasp into her own embrace. John stepped aside at once. "Are you hurt? Did you see it happen?"

"No," came the shuddering, but definite voice. "I'd decided to go see if the house elves had any leftovers I could feed my cat, but when I got here –" her hand spasmed in the direction of the corpse.

Professor Smith was acting as peculiarly as Sherlock had, bending over the body, sniffing the air around the corpse, shining what appeared to be a small torch around, though why he didn't just use the wand light was beyond John. Sherlock was edging to the side, eyeing the sides of the corridor, apparently searching for something.

"I think the children should go. Pomona, why don't you take Miss Molly to the hospital wing?" He paused and waited until she looked up. "Molly Hooper, wasn't it?"

She nodded, scrubbing at her cheeks with the handkerchief Professor Sprout had just conjured, still pale but infinitely calmer. Smith smiled and chucked her gently under the chin.

"You've been a big help. Now go on with Professor Sprout. Madame Pomfrey will give you something for the shock."

They turned to go and McGonagall was about two steps behind, shepherding the two boys away.

"Not a word of this to anyone, understand? We'll be dealing with the situation right away and no point in sending people into a panic on the first day of classes." She said the words lightly, but there was no mistaking the iron intent behind them.

The secrecy didn't set right with John, who had had quite enough of such foolishness last year. To his surprise, Sherlock nodded.

"Of course, Professor," he said, with an almost too-perfect blend of seriousness and pleasantry. "We'll just collect our things from the library and be off. I'm sure they need you back there."

No sooner had McGonagall disappeared around the corner than Sherlock burst into activity. John, who had been mentally preparing himself for the trek up to the dormitories and the probable dreams he would have to deal with, was nearly dizzy with the sudden dashes from one wall to another - now kneeling on a flagstone and shining his wand light on it, now examining the lamp holder on the right wall.

"It's guttering differently that the others," Sherlock said in answer to John's raised eyebrows. "Look," he gestured as John continued to stare. "See? Those scratches on the sconce are fresh – look at the bright edges. It came this way."

John, who had been craning to see the miniscule marks, backed away immediately, wand leaping to his hand. "The thing that did that to Chimmy?"

"Chimmy?"

"The elf, Sherlock, the elf," John snapped. "The thing that ripped it to shreds came this way?"

Sherlock nodded, eyes scanning the floor of the entrance hall. "And it's still here."

John made a noise that was meant to be "what?" but came out in a strangled tumble of sound.

"Did you hear a door close? Or a crash? Glass breaking? Or something with claws this big – " Sherlock spread his hands about 10 inches. " – going up the stairs? It hasn't left the castle."

"The thing could have killed him earlier and –"

"The blood had barely begun to congeal," Sherlock cut across him, now searching up the walls with his wand lit. "It's a good jumper and climber," he said, pointing at a spot several feet above their heads.

John squinted, but couldn't discern anything on the rough surface. But he was learning that this boy didn't take kindly to stopping to explain.

"Alright, so it's what – in the rafters?" He tightened his grip on the wand, bracing himself.

Sherlock nodded, pointing his wand at the deep shadows on the cavernous ceiling. "Lumos maxima!"

The light shot through the hall, filling it completely. John took aim at – nothing. Every detail of the ceiling was revealed. No monster crouched among the rafters or cowered in the corner.

"But –" Sherlock frowned, taking several paces in different directions and peering upward. "It has to still be here."

The sound of footsteps cut him off. Professor Smith was striding toward them, brow furrowed. Sherlock extinguished his wand just as Smith noticed them and frowned.

"Now, boys, there's nothing more to see. If you're expecting more juicy details, you're out of luck."

"We were just talking," Sherlock said with shrug. "Any idea what did it?"

"I've managed to rule out Vashta Nerada and –" he cut himself off, smiling suddenly. "No, not yet. Certainly not any of us."

John and Sherlock exchanged a look. He'd sounded so unsure as he said it.

"Well," Smith said, clapping his hands together. "Off to your dormitories, the both of you. It's almost curfew."

"But –" John began, casting a glance up at the ceiling. Sherlock shook his head and yanked on his sleeve.

"Come on, John," he urged. "Madame Pince will be closing the library and I've left all my books there."

"You realize it could attack again – could kill Professor Smith right now, don't you?" John hissed.

"Unlikely. If it wanted more, it had two fine young helpings right in front of it all this time." Sherlock shook his head. "It won't strike again tonight. Besides, if it did, that would be an interesting development."


	6. Chapter 5: A Visit from Mycroft

"Forgive the seeming rudeness, but can you explain to me how you managed to allow another incident to occur in the presence of students?"

Mycroft Holmes disliked traveling from London. Work tended to pile up unconscionably fast and late nights at the office were not on his agenda. But Shacklebolt had put him in charge of the project, which made the alien leaning tensely against the Defense Against the Dark Arts desk his problem. It didn't help that they'd left it two days before informing him.

"You made the mistake of giving me a full-time job," the Doctor said. "I'm in a castle that, frankly, makes Pan's labyrinth look like a garden maze – and I should know, I've been through it twice – and I'm teaching 12 classes of a subject I never studied because I, unlike Professor John Smith, am not a wizard. So you'll forgive me if I seem lazy, but I've been a bit preoccupied."

"Minerva McGonagall informs me that your… inexperience," he said delicately, "with a wand has been remarked upon."

"Well, it's no sonic screwdriver."

He was trying to turn it into a joke, and Mycroft was not amused. "We were assured that your DNA was compatible with our powers," he said, keeping his voice dangerously low.

"Technically, yes, but I've been bouncing around the universe for 900 years and I've never touched a wand. It's a skill, and I haven't been in training since I was 11, unlike you lot."

Mycroft merely stood still, observing. The Doctor frowned, shifting uncomfortably in his robes.

"I'm sorry, Mr. Holmes, but if you want me to continue this charade, it's going to take time."

"You're a time lord. You could search the whole castle and grounds and be back in time to give your next lecture."

"Too risky. The TARDIS is reacting to the magic in the atmosphere. I have no idea if I could be precise enough to make it back within minutes or even hours. I could simply disappear for two weeks, or till final exams in June. Now, while that means a pile of essays I wouldn't have to grade, I don't think it solves our problem."

Mycroft swallowed several more vitriolic replies before saying, "If you're not going to do anything, we -"

"I never said I wasn't doing anything," the Doctor protested, smiling suddenly. "That attack was actually a big help – I've got new information to work with. Type of teeth and claws, that sort of thing. It narrows it down, just knowing it's got teeth and claws – believe me. Just be patient, I'm working on it."

"Yes, as is my little brother," Mycroft said icily. "I won't have him mixed up in this."

"Sherlock is a determined, intelligent young man. I sincerely doubt your permission or disapproval makes a whit of difference to him."

The Doctor's matter-of-fact tone was vaguely insulting. As if this man could understand Sherlock after mere days. Mycroft drew in a slow breath and fixed him with one of his more intimidating glares. "So fix it before he, or anyone else, gets hurt."

The Doctor returned his gaze without flinching. "That's the plan."

The first students in the 3th year Ravenclaw/Hufflepuff section of the class were queuing outside the door as he left. Mycroft checked his watch. The 7th years who were not in Ancient Runes had a free period, and he had one other item of business to take care of before tea with Professor McGonagall.

John Watson was sitting under a tree a ways away from the others. Mycroft recognized the boy from his files, even without the extra research he'd done the previous night. A Muggleborn who didn't know how to keep his head down. Not a suitable companion for Sherlock. He sighed, looking at the sunlit yard with its clusters of students. This was not the ideal location, but he was short on time.

He moved forward, letting his shadow fall on John's parchment. The boy looked up, irritated, expression fading to wary as he took in the strange man before him.

"Mr. Watson."

"Yes?"

Mycroft didn't miss the fact that John had reached for his wand. The St. Mungo's files hadn't been wrong.

"I'd like to have a word with you. Walk with me."

A stubborn vertical line appeared between his eyebrows. "What if I choose not to?"

"That would be unfortunate for you," Mycroft said calmly, propping himself up on his brolly and waiting.

John eyed him another moment and picked up his quill. "So would not finishing this essay."

Mycroft flicked his wand and the paper flew neatly into his hand.

"Oh, very mature," John mocked.

"This won't take long." He waited, but John stayed put. "It's to do with Sherlock Holmes."

On the whole, John Watson reacted much less than Mycroft had anticipated. His eyes widened only for a fraction of a second, but it had been enough for Mycroft to realized he'd hooked his man. John grabbed his cane and stood, making it clear as he did so that he was not amused or intimidated by the man before him.

"How do you know Sherlock?" John asked, lengthening his stride to the point Mycroft knew had to cause him pain. He didn't lag as Mycroft continued at his usual pace into the castle and led him into an empty classroom.

"I've known him for years," Mycroft said finally, laying his umbrella on a desk and turning to face John.

"Friend?" John bit out, leaning against his cane.

"You could say that. The closest thing to a friend he's ever had."

"And that is?"

"An enemy."

That got a definite reaction. John's hand tightened on his wand, eyebrows coming down as his eyes narrowed. It was conceivable that this look had cowed his peers before now. Protective, Mycroft would grant him. Still, these hair-trigger reactions would only make Sherlock worse. Mycroft put on his most dangerous smile.

"Come now, you've known him for three days and you must have seen it. How many friends do you imagine he has?"

"You said this wouldn't take long."

"It won't. Stay away from Sherlock Holmes."

He actually snorted. Mycroft had to admire that. "I'm sorry Mr. – whoever you are, but exactly how is it your business who my homework partner is?"

"I'm a concerned party."

"Concerned how?" John's voice was rising subtly.

The fool wasn't going to budge, that much was certain. Mycroft switched tacks.

"I worry about him. He's am impulsive child and his antics are likely to get him or someone around him killed. I'd like to avoid that if possible."

"Still not seeing where that keeps me from writing research essays with him. If you're so concerned about him, talk to him."

"My involvement would be unwelcome –"

"Shocking."

" – to him, but I do know what's best for him," Mycroft finished smoothly, ignoring the interruption. He cocked his head a few degrees, letting his features smooth into a beneficent smile. "You've had a taste of leadership, Mr. Watson. You understand making unpopular decisions for the greater good, don't you?"

For the first time, the calm contempt slipped, showing the teenage boy's frightened eyes. It was gone in a moment, carefully hidden beneath disinterest.

"Look," John said, spacing his words carefully. "I don't know or care who you are, or what information you think you have about me, or Sherlock, or any other person in this castle. You don't scare me, and I think I'm old enough to pick my own mates."

"Your loyalty is given remarkably fast," Mycroft commented.

"No, I just don't' like you." John's voice was deadpan, the expression on his face blandly polite. "I don't get on with people who try to tell me who is and isn't acceptable company."

Yes. Muggleborn John would be touchy about that. Mycroft adjusted again, begrudgingly impressed with the boy.

"Very well. How about a different arrangement?" He fished in his pocket for a money bag. "I have need of a good set of eyes –"

"Don't." John had raised a hand in clear warning.

Mycroft actually paused, hand halfway out of his pocket, to look at him. John shook his head and extended the hand, palm up.

"I'll have my essay back now."

"I haven't mentioned a sum."

"And you're not going to," John said calmly. "The essay, please."

There was a chance, a faint one, that a personality this immutable could withstand his brother. Whatever else might happen, Mycroft didn't have to worry about this boy being swayed by the talk that always surrounded Sherlock. Rather to his own surprise, he withdrew the parchment and sent it floating into John's outstretched hand.

"Choose your side well, John Watson," he said, brushing past him to the door.

It had been a singularly unproductive trip.


	7. Chapter 6: Following the Clues

"Sherlock?"

The boy was leaning back in his chair, eyes unfocused, fingers playing through the air in odd patterns.

"Sherlock!" By the fifth time, he seemed to have heard.

"Hm? Oh, John." Sherlock sounded vaguely disappointed.

John repositioned his cane and looked around the empty third-floor classroom, waiting for all of Sherlock's attention to focus within the room. "I just had an interesting little chat."

"Not a Graphorn," Sherlock mumbled. "Chat? With whom?"

"Friend of yours."

Sherlock's eyes snapped open. "Friend? What friend?"

"Well, he said an enemy."

"Oh," Sherlock looked relieved. "Which one? Anderson?"

"He didn't give his name. Tall bloke, skinny, sort of gingery hair? Adult, but not a teacher. Must be a visitor or something. Sound familiar?" He asked as Sherlock rolled his eyes.

"Yes."

John waited, but he seemed in no hurry to elaborate. "Who?"

"The most dangerous man you've ever met and not my problem just now. What sort of creature has a taste for house elf?"

"I've been over it a dozen times since the other night, and it makes no sense –"

The door opened and Lindsay and Molly peered in.

"Oh, sorry," Molly said immediately. "We were just looking for a place to review our essay," she held up a roll of parchment.

"Come on in," John invited, ignored Sherlock's little snort of disapproval. "We're practically done anyway."

Sherlock rolled his eyes and looked out the window, but just as quickly had snapped his head back around. "You. You were the one who found the elf, weren't you?"

Molly cut her eyes around the room, suddenly fidgety. "Yes."

"Sherlock," John warned. "This may not be the time."

"I know about it," Lindsay announced. "Molly told me yesterday."

Molly looked abashed. "It just slipped out. Besides, she's the only one I've talked to about it."

John nodded his understanding. Sherlock didn't seem to be paying attention.

"And you?" he demanded, turning to Lindsay.

"It's Lindsay. Remember? I introduced you yesterday in Herbology? She was in our group for the sopophorous beans."

Sherlock stared blankly. John was only marginally surprised, as Sherlock had spent most of the class muttering to himself about Professor Sprout's obvious preoccupation with her diminished mandrake population and its effect on her lesson planning. He started to introduce them again, only to realize that Sherlock once again was talking to himself.

"It doesn't make sense!"

"What doesn't?" Lindsay asked, turning a chair backwards and seating herself on it.

"There are no creatures in our world that have such a strong taste for elf meat that it will sneak into a school full of wizards and crammed with easier targets, eat one elf and vanish –"

His eyes slid out of focus, whole body frozen, one hand mis-dismissive wave.

"Oh…"

"What?" John asked, wincing at himself. The word was already becoming overused.

"It vanished. Don't you see? We looked everywhere it possibly could have gone. We didn't see any signs of concealment or any place where it could have gone out of the castle. The ghosts haven't seen or heard anything, and they assure me that the staff haven't found anything either."

"The ghosts…" John stopped himself before parroting yet another sentence. "Right then, what does that mean?"

Sherlock's grin slipped. "You don't see?" John and Molly shook their heads. He seemed to deflate. "You look like a pair of Bundimuns. Is it nice not being me?"

"It has some way of making itself invisible, "Lindsay interrupted. She continued slowly, stringing her ideas together. "If there have been absolutely no signs, it had to have left no signs, which means invisibility or apparition."

"But you can't apparate within the castle," Molly said, catching the rising comprehension.

"Right, and we're almost certain this was a creature, not a wizard. At least, I hope so," Lindsay continued. "So, if that's true, an invisibility cloak isn't looking likely. What options does that leave?"

Sherlock interrupted, looking a bit piqued. "A magical creature that can turn itself invisible and has an apparently intense craving for house elf flesh."

"Well, that narrows it down," John said.

"Yes, quite a bit," Sherlock said. "It doesn't exist."

The four of them were silent for a moment, then John offered. "I could go talk to Hagrid on my free period. He'd know about a creature that dangerous."

"Hagrid is about as reliable as Trelawney's tea leaves when it comes to information," Sherlock said. "I might have a different solution. Another Ravenclaw – Victor Trevor – is doing an independent study this term about the use of potions to identify wizarding criminals. He's developed some tests very similar to what muggles use for DNA testing. I have a sample from the bite marks on the elf. Victor will jump at the chance to try out his tests, and Professor Slughorn allows him in the potions laboratory unsupervised."

"And not you? I'm stunned," Lindsay said drily.

Sherlock shot her a look. "Considering you are in your seventh year and still haven't perfected a shield charm, that must have been a regular occurrence."

"I imagine you had to learn that one by primary school or you never would have survived long enough to get to Hogwarts."

"Alright, you two," John interrupted. "Enough. And what's this about a shield charm?"

Sherlock rolled his eyes. "She's wearing foundation. She wasn't wearing any yesterday, so I assume make up is not a daily habit with her. That makes it important. It's especially heavy on the right side of her jaw. Most girls apply makeup in strokes going down the face, so for there to be excess under the jaw would have to be intentional. If you look closer, there's some redness under the foundation – a fairly wide swath. Not a fingernail scratch , then. Regardless of how clumsy a person is, it's hardly reasonable to assume they would trip and scrape their chin beyond age 4, but any more serious fall would have left more serious injuries. Obvious conclusion: this wasn't self-inflicted. I can think of six minor jinxes or hexes that would cause a person to fall forward without the ability to catch themselves, and judging by her friendship with you, John, I'm guessing she also made enemies last year. The fact that the injury happened at all tells me her shield charm is not the quickest or strongest."

John had stopped listening several sentences back and was examining the scrape with care over Lindsay's protests.

"Shut it and let me make sure there's nothing more serious the matter," John commanded, siphoning off the makeup with his wand. The skin was red and raw, but appeared to have begun healing already and had none of the telltale signs of a cursed wound.

"You think I didn't already check?" Lindsay asked as he leaned back. "It was Alexander Mulciber who cast it when I met him coming around a corner. I wasn't going to take any chances."

John suppressed a sudden urge to laugh. Mulciber had been the Carrows' pet last year, and by extension, the particular target of DA pranks. Small wonder he'd jinxed Linsday. "I can fix that up for you," he said, waving his wand in a diagonal pattern so the redness receded and the skin closed itself. "There. Did you give him anything in return?"

Lindsay smirked, but said nothing.

"Mulciber was one of the two who jumped me on the train," Sherlock said.

"Not that I think we have time for the full list – but what made them fight you?" John asked.

"Well, the immediate cause was my question if Moran's girlfriend knew her rival was Mulciber, but there were other inciting comments as well. People always get so offended by the truth."

John was relieved he was not the only one staring at the skinny 15-year-old. Lindsay was right; it was something of a miracle the boy had lived this long.

"Well," Sherlock said, rubbing his hands together and bounding to his feet with sudden energy. "I think I'll head back to the dormitory and collect that sample to give to Victor."

He had only gone a few paces when the sound of many hurrying feet in the corridor informed them that the free period was over. They were all headed to the same classroom, but Sherlock hung back, letting the girls go on ahead.

"Your friend should be more careful," he said, his voice more annoyed than concerned. "Slytherin House as a whole is spoiling for a fight – anything to cause trouble in the other houses, but especially Gryffindor."

John shrugged. "Lindsay can take care of herself. There's a reason her shield charm isn't her quickest."

"I was thinking more logistically. I don't doubt McGonagall would slap stricter regulations in place in a moment if she thought it would help keep the students safe. The last thing we need is a duel in the courtyard. I have things I need to do, places I need to examine in regards to this attack, and I can do that much easier without bothering with extra rules to duck around."

"What places?"

Sherlock waited until a trio of Slytherins had shoved past. "I want to have another go at the entrance hall when no one else is around. I have an idea which might give us another option besides invisibility, but I need to be certain no one will interrupt me."

Their chance came that evening. Sherlock showed up at the Gryffindor table during pudding, plopping himself alongside John and ignoring Lindsay as he spoke rapid-fire.

"There's a mandatory meeting in each common room tonight at 8. Meet me in the entrance hall at 8:05 and we can have a look round."

John laid down his spoon. "A mandatory meeting," he said slowly, cutting his eyes to Lindsay. "Right, then, I'll just ask Professor Smith very nicely if I can skive off, shall I?"

Sherlock rolled his eyes. "Just sneak out."

"The portrait hole doesn't lend itself to sneaking," Lindsay said. "The Fat Lady would rat on you in 2 seconds."

Sherlock looked startled, as if he hadn't noticed Lindsay before now. "So think of some excuse to tell her."

"What we really need is a diversion," Lindsay countered. "If we could distract everyone long enough to get the portrait hole open and closed, the Fat Lady might be convinced to keep quiet when we get back. She loves a chance to spy on ruckus in the common room."

"We?" Sherlock asked icily.

"Yes," John said before Lindsay could reply. "Her plan, she gets to be a part. Besides, another set of eyes can't hurt."

Sherlock very nearly pouted. "What's the diversion, then?"

Lindsay smiled. "Peeves."

The preparation was relatively simple. Peeves was more than eager to abandon his post at the library entrance, where he had been tossing ink pellets at anyone coming or going, and follow them to the Gryffindor common room, where he sneaked in under John's robe hem. The idea of pranking the new professor seemed to excite him more than anything since the Weasley twins made their flashy exit from the school three years earlier. The only difficulty came in keeping him in check until the proper moment. The poltergeist finally agreed that his access to the common room was reward enough. He'd been scrupulously kept out of the dormitories for all four houses since the founding of the school, a fact that was making John uneasy.

"How do we get him out?" he hissed as he took his place in a chair near the portrait hole.

Lindsay gave a miniscule shrug. "Either they'll have taken care of it by the time we get back or…" she paused and a shade of disquiet fell across her face. "We'll figure it out. Maybe get him into Slytherin in exchange for getting out of Gryffindor."

Professor Smith walked in, greeting their worried faces with a wide smile. "Why all the gloom and doom? It's a meeting, not an execution. Here!" He twirled his wand impressively in the air. Nothing happened. With a resigned sigh, he reached into the teacher's robe he still wore and pulled out a large bag from Honeydukes. "Here, Peakes, start this around, won't you?"

He waited until the first cluster of students had collected their toffees before proceeding with roll call. John, eyes on the curtain where Peeves lay in wait, listened impatiently for the W's. They would be late to meet Sherlock and somehow he didn't like to think of the boy wandering around the hall doing Merlin knew what by himself.

"John Watson."

"Present," he said with more enthusiasm than necessary. Lindsay dug his elbow surreptitiously into his ribs, but he knew better than to react while Smith was still watching.

"Constance Willinsnope."

"Present."

Constance was behind Smith. Lindsay and John positioned themselves closer to the portrait hole as he turned his back to them.

"Oi," John hissed in Lindsay's ear. "That hurt."

"Then stop acting like you've never sneaked out before, Frankie First-Year," Lindsay said, giving the curtain a firm nod.

Peeves took the signal. The air in the common room was suddenly bespeckled with small black balls, then they dropped, splattering the students below with ink. Over the Gryffindors' outraged cried and Professor Smith's inarticulate shouts rose Peeves' cackle as he zoomed about, dropping his second shower of pellets. John and Lindsay acknowledged his flourishing salute and ducked out the portrait hole.


	8. Chapter 7: Stairs

Sherlock was crouching in the far north corner of the hall when they arrived.

"Stay for the whole meeting?" he asked without looking up.

"Just took us a bit to get out the door," John clarified with a hint of irritation. "You can't have been waiting long. Now, what would you like us to do?'

"At the moment – shut up."

It took a tight grip on Lindsay's wand arm to stifle her reaction to the directive. She was strong, but John held on, silently daring her to try anything. She'd just begun another attempt to wrench her wand free when Sherlock rose and dusted his hands.

"No hidden doorways in this entire chamber," he announced. "I've sounded each wall 15 feet up. Nothing. Not even a mouse hole. So, that leaves the question – how did it get out? One can't expect it to skulk in the shadows of a place this crowded all the time."

"So it waited till we left and climbed down," John began. "Then… what? Went out the front door? Up the stairs?"

"What if it went up, but not by way of the stairs?" Lindsay asked.

Sherlock looked slightly miffed. "Just what I thought. The scratches on the stone lead to the rafters. It's hard to see from this distance, but I believe I can make out some scratches on the beam fourth from the right. If that's the case, it could have gone along the rafters down any of these corridors."

"What good would that do it? It would still be trapped inside," Lindsay countered.

"Not necessarily," Sherlock said with no small amount of smugness.

He cocked an eyebrow at Lindsay, daring her to answer. John crossed his arms and watched the two of them, wondering if either had the slightest idea how amusing they looked. Sherlock raised his chin in victory and opened his mouth.

"The balistrarias," Lindsay blurted. "The balistrarias on the astronomy tower."

"Sorry, the what?" John asked before Sherlock could reply.

"Narrow windows in the stonework, open air, originally intended for archers as battle stations," Sherlock answered rapid-fire. "If the creature can fit through them, it would be the easiest way to get in and out of the castle and avoid contact with most of us."

"Well, let's check," Lindsay said, taking off down the corridor before Sherlock had fairly finished speaking.

Sherlock responded by dashing ahead. The two of them kept pace, John tapping along behind, all the way to the spiral stone staircase that led up to the astronomy tower. Lindsay slowed at the stairs, glancing back at John. Sherlock was several stairs up before he realized he was alone.

John jogged the last few yards, feeling their eyes on him.

"You could be a lookout," Lindsay suggested. "You probably shouldn't stress your leg –"

"Damn my leg!" John snapped. Both of them stared. "Sorry. It's just… I'm fine. I'm perfectly capable of walking up stairs. Sorry for holding you up." The apology was sour in his mouth.

"It's okay, we don't even know if this is the right way," Lindsay assured him.

"Wrong."

Sherlock was shining his wand light up at the rafters. He looked down at them, grinning. "Scratches. It came this way."

He came down two steps. "The first balistraria is two flights up. We shouldn't need a lookout down here. We'll hear them coming long before there's any visual confirmation. Both of you keep your eyes open, and if you see anything, just say so and don't touch it." He whirled around and started back up the steps, taking them two at a time. "Nothing worse than people spoiling evidence."

"Oh, he grows on you," Lindsay said in an undertone to John as they came up at their own, slower pace. "I can see why you wanted to come tonight."

"Do you think it's a good idea to leave alone to his own devices?"

"I managed quite well before I met you, John Watson," Sherlock's voice floated to the from around the curve in the stairs. "I'll thank you to leave the protective big brother bit for your actual younger siblings. I've already got one to plague me. And Miss Lovejoy, there was no compulsion for either of you to come."

They caught up and found him actually halfway up the wall, having slipped his shoes off and used his toes to find niches in the stone.

"If you did stuff like this alone, you must have been a frequent visitor in St. Mungo's," John said, setting his cane against the wall and drawing his wand.

Sherlock looked down in confusion. "What are you doing?"

"Keeping you from dying." John waved his wand in a broad circle under the spot where Sherlock clung lizard-like to the wall. "Impervioscurrsus."

"I don't know that spell," Sherlock said in real interest, staring down at the transparent barrier that now stretched beneath him.

"That's because Terry Boot invented it for Dumbledore's Army last year," John said, a trifle impatiently. "It's a bit like landing in a custard – you just sink through and land gently on floor, no matter how fast you were going before."

"Why not just use feather light?" Sherlock asked, edging himself a few inches higher on the wall. The window was almost within reach.

"Because we needed a spell that covered multiple people with ease."

Lindsay's voice broke in. "Have you noticed the scratches on the rafters continue?"

John and Sherlock turned to look at her. She was disappearing around the turn of the stairs.

"There are claw marks on the stone here," Sherlock countered. He turned back to the wall and examined the patterns. "They lead right to the window. You're saying it didn't go out here?"

"Hang on, I'm checking."

Sherlock leaned out from the wall to get a different perspective on the marks. The silence had only settled about 10 seconds when Sherlock let out an impatient sigh. John looked up in time to see his fingers slip off a too-small crevice, and Sherlock drop from the face of the wall. The clear layer of magical protection caught him and he slid through it with a slight squelching sound to the stone steps below. John cocked his head to the right and waited as Sherlock dusted himself off and settled his robes.

"You're welcome," he said pointedly, following the stairs around the curve to where Lindsay was examining the wall.

"The marks are different by this window," she said, eyes still on the wall.

Sherlock dove closer, nose nearly touching the stones. "It backtracked, but only just here. Like it was confused or scared." He grabbed the first jutting stone he could grasp and hoisted himself up again. "Wait." He pointed his lit wand at the wall, smiling suddenly. "These claw marks are smaller. At least 1/16th of an inch."

"Naturally. Why didn't we see that?" John asked with good-natured sarcasm.

"So there are two of them?" Lindsay asked.

"And one is smaller than the other. Male and female or parent and child? Closeness of size suggests either an adult female or a nearly grown child. Statistically, more likely to be child, as one mate would do the hunting while the other watched the young. So this one is ready to be taken on hunting trips – but it didn't go down to the corridor with its mummy or daddy. Why?"

Sherlock was speaking so fast that it took a few seconds for the others to catch up with his words.

"It got scared?" John asked.

"Or something kept it from going along. If I knew what creature I was dealing with, I'd be better able to judge," Sherlock said, inching closer to the balistraria. "Regardless, two creatures definitely came through this balistraria. Vial." His outstretched hand was an order.

John conjured one and levitated it up to Sherlock. The Ravenclaw transferred his wand to his teeth and used one of the fingers from the hand clutching the wall to scrape something from the crevice beside the window.

"What is it?" John asked.

Sherlock answered around the wand. "Not sure. I'll have to look at it closer whe –"

A small sound from above cut him off. They all turned to face the rafters, only to realize the sound was coming from higher up the staircase.

"Mrs. Norris!" Lindsay exclaimed. "Filch is coming!"

Sherlock dropped from the wall with surprising agility, landing in a half crouch that set him in an excellent position to run. John had already bolted down the steps. It took him three turns in the stairwell to realize the others were not at his heels or passing him. He glanced back to see Sherlock saying something to Lindsay as they trotted along. She nodded and bolted back around the corner. Sherlock caught up with John in three long strides and pulled him along.

"Where's Lindsay going?" John asked, skidding to a halt.

"She's coming, I swear. Now go!" Sherlock snapped, grabbing John's arm and yanking.

John planted his feet just in time to see Lindsay barreling around the corner.

"Go on!" She snapped in an undertone, galloping past them both and heading for the corridor, robes billowing behind her. Another, uneven set of footsteps from above sent the boys after her.

Sherlock regained the lead just in time to duck through a door pretending to be solid wall onto a little-used staircase that led up to the fourth floor. From there they took a chance on the main stairs. Filch was nowhere to be seen above or below. Sherlock, still in the lead, sent a freezing charm at the moving staircase, stopping it at the landing they needed. They dashed up and waited just long enough for Sherlock to freeze the next two sets of stairs, which lead them up to the seventh floor.

They arrived on the landing of Gryffindor corridor, breathless, laughing, and unfollowed. Sherlock pulled his shoes from inside his robes and slipped them back on. John leaned against the wall, gulping at the air. He'd done his best to rebuild his stamina since the weeks spent in hospital, but he wasn't quite up to a sprint across the castle. His leg would never forgive him.

His cane. "I've left my cane on the stairs," John exclaimed, bolting up from the wall.

Lindsay and Sherlock exchanged a look, still chuckling. It took a moment for them to focus back on him and read the askance look on his face.

"Did you miss it?" Lindsay asked.

John spouted the beginning syllables of several sentences before settling on, "That was adrenaline. Fight or flight, or some such."

"How about now?" Sherlock offered. He tossed the vial he'd gathered at John, but far to the right.

John sidestepped instinctively to catch it, landing with all his weight on the leg that had refused to support him since May. He half-braced himself, but the knee didn't buckle and the muscles felt as solid as – as they had before the battle. During the battle, too, if he was honest. A slow, reluctant grin fought itself free from his tense facial muscles. He tossed the vial back to Sherlock, who caught it with a cat-like controlled swipe and laughed again.

"Just proving a point."

"But my cane," John said, suddenly sober. "Filch will have found it."

Lindsay pulled it from within her robes. "Sherlock told me to go back for it."

John took it, hefting it slightly from hand to hand. It already felt like an unwelcome intrusion. He turned down the hallway. "Well, then. Do you think Madam Pomfrey will release me for the Quidditch tryouts?

The Fat Lady interrupted before either of them could answer. "What mischief have you been up to?" she demanded with none of her usual conspiratorial tone.

The three stared at one another, groping for an explanation, when the portrait hole swung open and an ink-bespattered Professor Smith stepped out. He folded his arms and stared at them, an effect which was somewhat spoiled by the large smear of ink above his eyebrows which gave him the look of having a uni-brow above the real ones.

"Any explanation?" he asked..

John ran through the options in his mind. The truth was out of the question, and any lie too far-fetched to make believable. He glanced over at the other two. Sherlock had drawn breath to speak three times, then stopped himself.

"Alright then," Smith said. "Detention. My office, Saturday morning, 9 a.m."

"But, sir," Lindsay blurted, looking a bit surprised at her own daring. "It's quidditch tryouts Saturday morning."

Smith seemed to consider. "I suppose I ought to make you come anyway, giving up a pleasure and all that…" he grinned, showing off an ink splatter that had managed to black a couple of teeth. "But I want a stupendous Gryffindor team. So go on to the tryouts. Let's make the detention 2 o'clock instead."

They all muttered their thanks, and Sherlock turned away to the Ravenclaw dormitory looking only slightly murderous.

"Oh, Watson, Lovejoy," Smith said, turning on his heel at the stairs. "Peeves is still in there. Nip him out before you go to bed, won't you?"


	9. Chapter 8: Eliminating the Impossible

Saturday morning dawned crisp and clear on an unexpected phenomenon. John Watson and Poppy Pomfrey arguing in the hospital wing.

"Look, it's fine!" John said, walking up and down the length of the room.

"I'm sorry, John, but I can't clear you," Madam Pomfrey said, genuine regret on her face. "I've already sent an owl to Healer Gillysmythe and he agrees."

"I've been walking around on it for three days without the cane. No pain, no cramps, no weakness. Healer Gillysmythe always said it was a mental thing."

"Yes, and that's what makes it so imperative that we continue to observe you. What caused this sudden turnaround?"

John stopped his energetic pacing and faced her, squaring his shoulders. "Why is that important?"

"Because we need to know how it affected you. If it's something that can be used to help other psychosomatic sufferers. If it's permanent. If you'll wake up tomorrow and your leg will be worse than ever."

Poppy had mirrored his aggressive stance, shoulders back, arms folded, chin down. John knew a lost cause when he saw one. Madam Pomfrey with her heels dug in was more frightening than a nest of acromantulas. He toyed momentarily with the idea of telling her exactly what caused the limp to disappear. He thought it likely she would keep his secret, and he technically would be serving time for it later that day. But the tale implicated others. He settled for a non-specific version of the story.

"I had a foot race up the stairs from the ground floor to the Gryffindor dormitory. Didn't miss my cane till I was at the top."

"What inspired you to sprint up seven flights of stairs? When I saw you Monday, coming down two flights to get here was a challenge. That's only five days past –"

"But the point is that it's gone now. Isn't that what you and Gillysmythe have been working for?'"

"Yes, and when enough time has passed that we're certain it won't come back, you'll be free to do whatever you wish. But I can't give you permission to spend hours on end on a broomstick dozens of feet off the ground. Quidditch is dangerous enough without the possibility of your leg giving out and you plummeting to your death. I'm a good healer, John, but I can't heal that."

It would be easier if he didn't know her so well. Poppy Pomfrey cared about keeping the students of Hogwarts safe. Nothing else in all the world could possibly matter as much as that – particularly not Quidditch. He'd been treated to a half hour lecture on the dangers of the sport when Snape had banned it last year. Madam Pomfrey had almost sent him a bottle of mead.

He sighed and leaned forward "Look, I've only got this one chance left to be on the Quidditch team. I've tried out every year I could and never made it. There's no guarantee I'll make it this time. But I want to try."

She wilted a little, holding his gaze. He could see the hesitation in her eyes.

"I'm sorry, John. No."

Sherlock was waiting outside the door, leaning against the wall and tapping his foot. "Well?"

"Let's go," John growled, taking the first flight of stairs two at a time.

Sherlock caught up by the sixth step. "The chances of you being on the team were never high, anyway. Ginny Weasley is captain, right? That means that every member of Gryffindor house who owns a broom will be out on the pitch. And you've tried out before, haven't you?"

"Yes, but the first time the Keeper position was available, I was a 4th year, and all the other people who tried out were older –" John let his voice trail off. "I didn't say she'd said no."

Sherlock merely looked at him. John had to admit it wasn't too difficult of a deduction. They reached the second floor landing and turned the corner to the next set of stairs when Sherlock spoke again.

"The probability is that you wouldn't have been selected this year, either. Given your lack of playing experience and the fact you haven't been on a broom in over five months, there are bound to be at least three players who would outfly you, probably more considering the Gryffindor proclivity for Quidditch. Madam Pomfrey probably saved you from a great embarrassment."

John stopped and turned to face Sherlock. The Ravenclaw stopped as well, one foot on the next step down, and looked at him expectantly. John didn't speak.

"What?" Sherlock asked. "I was just stating facts."

"Well, stop."

"It's nothing about you," Sherlock said, his tone more scornful than apologetic. "It's just probabilities. Why are people always so quick to think everything is about them?"

John started down the stairs again, giving the sarcasm free rein. "Because we're all incredibly self-centered. But thank goodness you're above all that."

He glanced over to see Sherlock's reaction, but the boy's attention had been caught by a student standing near the foot of the stairs. John's brow furrowed as he squinted down at the boy. His robe was trimmed with Slytherin green, and he had a somehow reptilian stance. Perhaps it was the way his head seemed to slide from side to side rather than turn, or the beady look of his black eyes, but John instinctively disliked him.

"Sherlock," the boy said, his Irish accent oddly threatening in the soft tones.

"Jim," Sherlock said, giving the widest fake smile John had ever seen. "I was wondering when I'd see you."

"Miss me that much?"

"Don't flatter yourself."

"Excuse me," John interrupted, disliking the subtle animosity. "Who are you?"

The boy stuck out his hand with a slight bow. "Jim Moriarty, hi."

"John Watson."

Jim let go of his hand and jerked his head at Sherlock. "Why are you with this one? Some sort of punishment?"

"He's my friend," Sherlock said, bristling.

"And we were just heading to the Quidditch pitch, so –" John tried to edge toward the door.

"Friend?" Moriarty grinned rather nastily at John and turned to Sherlock. "I didn't think you bothered yourself with ordinary people."

"Don't you have some sort of plotting to do?" Sherlock asked, rolling his eyes. "Some prank to pull, or argument to start, or anything?"

"Bored with me already? That won't do, Sherlock." The Slytherin gave another slow, skin-crawling grin and backed away, hands in his pockets. "I'll be seeing you."

John and Sherlock stood stock still until he entered the Great Hall, apparently intent on catching the tail end of breakfast.

"Who the bloody hell was that?" John asked, his voice strangely quiet to his ears.

"Jim Moriarty," Sherlock said, folding his arms across his chest in an almost defiant way. "We've run into each other a few times. He likes to cause trouble where he can – mostly arranges other people's dirty work. If you have someone you want to get even with or generally make miserable, you talk to Jim Moriarty and he either does it or arranges for it to be done. I've managed to find proof against a couple of his goons in the past, but never Moriarty himself. He's clever that way."

There was no mistaking the note of begrudging respect in Sherlock's voice. He was impressed with the Slytherin, and John thought he knew why. It would take an extremely clever boy to leave no clues that Sherlock could find, and Sherlock would have no choice but to find that fascinating. John wasn't sure what was more disconcerting: the fact that Sherlock seemed somehow delighted in Moriarty's talents, or the idea that this boy had been operating in the school last year and the DA had known nothing about him.

"Well," John said as the silence lingered. Sherlock was still looking at the entrance to the Great Hall. "Shall we head down to the pitch?"

"Why? You're not going to try out."

"Because one of my best friends is still going to be flying and I want to be there to see it."

Sherlock looked at him as if he was speaking a foreign language. "Sentiment," he said, the word almost a question.

John sighed. "You could call it that."

He was somewhat surprised when Sherlock nodded and fell in step with him. They headed across the lawn and down to the pitch, where figures where already darting through the air. John counted at least 12, which meant that Sherlock was right – most of Gryffindor house would be out. He wouldn't go so far as to say that Sherlock was also right about him ending up embarrassing himself, but it was, all in all, perhaps best. The knowledge irritated him more than it soothed him.

They were passing the greenhouses when another student came running out to meet them. John had only processed the fact that his robes were trimmed in blue when Sherlock recognized him.

"Victor, surprised to see you out this early."

The boy brushed back his long brown hair and grinned. "Had some research to do. I wanted to tell you that the potions matured on that sample you gave me. I wrote out some findings, but you won't be happy."

Sherlock took the thin roll of parchment and opened it, brow furrowing. "Are you sure?" he asked, looking up.

"Positive. I even duplicated the substance and ran two tests to check," Victor said. "It doesn't match up to any creature in Wizarding Records. I went through the appendices of Fantastic Beasts three times last night. The best I can figure is that it's some sort of hybrid, probably something illegal. Hagrid, do you think?"

Sherlock nodded.

"Now wait just a minute," John protested. "Just because it might be a hybrid beast doesn't necessarily mean that it's of Hagrid's making. We have the entire Forbidden Forest full of creatures that we don't know about right at our doorstep."

Both Ravenclaws stared at him. John straightened his shoulders and endured the scrutiny. "It's true, you know. Besides, Hagrid has been busy helping rebuild the castle all summer. I sincerely doubt he had time to do any interspecies experiments."

Sherlock raised an eyebrow. "Very good, John. Fair reasoning. Of course, you're leaving out the fact that Hagrid has access to a great number of magical creatures, and it is quite possible for them to… create hybrids without his encouragement. Regardless, the fact remains that Hagrid has a reputation for trying odd experiments, and rather welcomes ."

"Let us all remember the Blast-Ended Skrewts," Victor interjected.

"Probability doesn't equal guilt," John maintained. "I think if Hagrid knew anything about this creature, it would have been taken care of by now. McGonagall wouldn't let him keep something that dangerous."

Victor looked at Sherlock and shook his head. "Skrewts."

John and Sherlock were still bickering about Hagrid's supposed guilt or innocence when they arrived at the pitch. The seeker tryouts were just ending, and the chasers were queuing up when they took their seats. John located Lindsay near the end of the line and gave a wave, which she returned distractedly.

"Look, all I'm saying is that we're making a huge assumption that is even is a hybrid, much less that it's one that originated here, and that Hagrid was involved," John said, watching the second batch of chasers dodging down the pitch.

"An assumption, yes, but a logical one. It fits. The reasoning is sound," Sherlock replied evenly. He'd taken a piece of parchment and quill from his robes and appeared to be working some sort of equation, taking information from the parchment Victor had given him. "This genetic code here –it's very similar to another one I've studied…"

John waited for him to continue, keeping one eye on the pitch. These chasers were pathetic. Lindsay was standing with her arms crossed, body tense. He couldn't see her expression, but, having played three-a-side Quidditch with her in the Room of Requirement last year, he could guess as to its meaning. He could almost hear the sighs of relief around the pitch with the group landed and the next set took to the air.

"Lacewing flies!" Sherlock exclaimed, holding up the parchment. "See? These markers – they are almost identical."

"So… a fly killed that house elf?" John asked, hoping the question was as insane as it sounded to him.

"No, no, of course not," Sherlock snapped. "It's just this one part here. The lacewing fly is an ingredient in polyjuice potion because it has the ability to change its skin pigmentation to reflect its surroundings. A bit like the disillusionment charm. Whatever this creature is, it has a similar ability."

"Do we have live lacewing flies on Hogwarts grounds?"

Sherlock considered for a moment. "I've never heard of them or seen them, but that doesn't mean they aren't around."

"But it does lower the likelihood that Hagrid is to blame, doesn't it?"

"What it does is convince me that whatever this is, it's not a typical hybrid. No creature that large just 'happened' to be crossed with a fly, and Hagrid isn't the type to do laboratory-style crosses. Which means –"

"Shush," John said suddenly. "Lindsay's going up."

The last group of six chasers mounted their brooms and took off to opposite sides of the center line. Ginny tossed the quaffle up, and Lindsay caught it on the tips of her fingers. She tucked it under her arm and took off, guiding her Cleansweep 10 down the pitch to the goalposts. She dodged under the reaching arm of another chaser, then swerved to the left to avoid another. One of the chasers on her side raised a hand as two from the other side came at her, but Lindsay did a hairpin turn and climb that left her above and behind them. She fed the ball off to the other girl, but a boy from the other side intercepted it right at the girl's fingers. Even from the stands, John could see Lindsay's body tighten in reaction. In the time it took him to groan in frustration, Lindsay had caught up to the boy and had swiped the quaffle almost out of his grasp. He just barely maintained his grip and spun around to get out of her reach.

"Oh, he's got a Nimbus. The turning radius on that thing is incredible," John said.

Sherlock looked at him blankly.

"Just… go back to your genetic markers and whoosy-what's-its. I'll let you know when the trials are over."

Sherlock bent his head over the paper almost docilely. John had to laugh as he returned his attention to the pitch. The boy was almost to the goalposts, but Lindsay was closing the gap between them faster than a Cleansweep 10 should be able to when matched against a Nimbus. He raised his arm to throw from outside the keeper's range, and Lindsay tapped the quaffle out of his hand. It dropped neatly into her own and she had spun around and was back down the pitch before the boy had lowered his arm. She scored a goal before anyone managed to catch up to her.

"She'll get in for sure," John said jubilantly, turning to Sherlock.

The Ravenclaw didn't look up from his parchment.

They didn't manage to catch up with Lindsay till lunch. Sherlock had insisted on leaving early to look up some obscure book in the library, and John, after a moment's hesitation, had followed. He hadn't been able to follow most of the information Sherlock shared from the book he'd found, but gathered it basically only confirmed what they already knew – there was no magical being that fit the criteria for the monster they sought.

When they entered the Great Hall, Sherlock surprised John by following him to the Gryffindor table and seating himself as though this were an everyday occurrence.

"Shouldn't you eat with the Ravenclaws?"

Sherlock shrugged. "It won't hurt the house elves to move one plate, and I don't like to eat with my classmates."

Lindsay dropped onto the bench across from them, a tired but ecstatic smile on her face.

"Well done!" John said warmly. "You were the best out there."

Lindsay's face tinged pink. "Thank you. Ginny said I'll have to learn a bit about sharing the quaffle, but she's excited to have me onboard."

"Not if sharing means the other people are going to give up possession," John objected. "But listen, we found out some stuff about the creature."

Sherlock looked up from the orange he was slowly peeling. "I'm not sure we can call it a creature anymore," he said, smiling at the confusion on their faces.

"Well, then, what was it? A person?" Lindsay asked.

"No."

"Plant?"

"No."

"Why don't you just tell us instead of going through this pointless guessing game?" John asked. "You know we'll never get it."

Sherlock put the orange down, laced his fingers under his chin and leaned closer to both of them. "It's not a magical being at all."

Lindsay and John looked at each other, but neither face held any answers.

"Say again?" John asked.

"Think about it," Sherlock said. "We've looked up every magical creature known to Wizardkind. We've actually had tests run on its DNA, and nothing. Not a single mention anywhere of anything that resembles this thing. When you've eliminated the impossible, whatever remains, however improbable, must be true."

"So, what, it's a… a Muggle beast?" John asked.

"A wizard who is an animagus?" Lindsay suggested.

"No, neither of those explain the skin pigmentation of the sample. And the bit I plucked out of the window last night was a completely clear hair. There are no creatures with clear fur. So, what does that leave us?" He waited, but both of them were looking at him. The right side of his mouth tipped up in a smirk. "Alien."


	10. Chapter 9: Aliens

"Would you pass me the um… jinx book?" John asked Lindsay, laying down his quill to massage his hand.

She passed _Jinxes for the Jinxed _and glanced up at Professor Smith, who was sitting at his desk drumming his fingers.

"Professor," she said tentatively. "Are you certain you want us making your lesson plans? I'd think you'd want to control your own curriculum."

"And how exactly does it fit as a punishment for sneaking out?" John muttered.

"No, no," Smith said, putting his feet up on the desk. "I think this is a completely fair punishment. And since I'm the teacher, you'll have to take my word for it." He gave a chuckle and rolled his wand between his fingers. "I could get used to saying that."

Sherlock looked up from the parchment he'd been working on for the last half hour, eyes narrowing. John glanced at the parchment, and nearly came out of his chair.

"Oi!" he hissed, jabbing Sherlock's arm with his elbow. "You're supposed to be working on the third year exercises. What's this?"

"Actually important things," Sherlock replied, edging the paper closer to John, his eyes still on Smith. "I need to talk to Professor Sinistra. She'll have knowledge of planets within easy traveling distance, and until I have more data I can't narrow our search further."

"You're asking for help?" Lindsay asked, amused.

Sherlock made a face at her. John glanced at Smith and gave a quick flick of his wand. _Muffliato. _Sherlock had caught the movement, and his eyes flashed from John to Professor Smith and back to the wand that now lay as it had before on the table. He gave a nod of approval and turned back to Lindsay.

"I have been known to do so when someone has information I do not."

"Yes, and you admit to that being the case? On multiple occasions?"

"I try not to clutter my brain with useless information."

"Apparently not so useless.

"If this is all you're going to talk about -" Sherlock made a production of taking a fresh sheet of parchment and pulling _Dark Beasts and Their Creative Killing Methods _toward him.

"Actually doing what we're supposed to be doing. Quite the threat," John observed mildly, leaning back over his lesson plan for the 5th years.

"I thought Gryffindors were supposed to be about breaking the rules. You two should have been in Hufflepuff," Sherlock muttered. "I bet you even asked Smith about what you missed in that mandatory meeting."

"They are implementing a zero-tolerance policy for inter-house heckling," Lindsay replied immediately, returning Sherlock's eyeroll with raised eyebrows.

"Are they serious?" John interrupted. "How are they going to police that when Quidditch season starts up?"

Lindsay shrugged. "McGonagall doesn't want any spats to get out of hand with everything so close behind us. Lots of students either lost family members or have family members now in Azkaban. It wouldn't take much to set them off."

"Rubbish," Sherlock said dismissively. "Victor's uncle is in Azkaban now, and he's never given it a second thought."

Both John and Lindsay had stilled at his words. Sherlock looked up at them in confusion. "What?"

"That's awful," Lindsay said quietly. "Must be hard to see everyone else so thrilled –"

"There are more students at Hogwarts now with a relative in Azkaban than not, I imagine, and you won't see a speck of trouble from any of them," Sherlock declared. "Most of Slytherin, and they won't dare make trouble for fear of getting chucked in, too.

"Are you sure?" John asked uneasily. "I mean, if I had an uncle who had just been sent to Azkaban, I wouldn't be fit within 100 yards of anyone I could hold responsible."

"So because someone you are related do did something that got him sent to Azkaban – justifiably so – you would take it out on your fellow students?" Sherlock asked.

"If I thought one of them could be partially responsible…" John took a moment to consider. "I don't like to think I'd do anything, but I know myself. There's a good chance someone would end up with a broken arm or sudden case of face tentacles or something."

Sherlock looked bewildered. "Sentiment?"

"Yes," John said, quite seriously this time. "And it's a powerful one."

"Well, the Slytherins I can't vouch for, Victor only cares about his potions. It's the only - " Sherlock began, but broke off as the door opened and Filch walked in.

Smith put his feet down immediately and rose to meet the caretaker halfway. Filch handed him a note and muttered something.

"Are you sure?" Smith asked. "I can come now –"

Filch shook his head, "Headmistress says you're not to interrupt anything. Just come when you've finished with this."

Smith nodded and turned back to his desk, brow furrowed. He looked up to see the three students staring at him, and responded with a wide grin. "How are those lesson plans coming along? Got the second quarter done yet?"

Sherlock startled both Lindsay and John by grabbing their completed pages and a respectable-sized stack marked with his own writing, and heading up to the desk.

"We're getting close," he said, putting on a very good imitation of a stereotypical Ravenclaw, thoroughly enthused with the intellectual task at hand. "It's been almost fun, going back through all these old topics. Almost makes me miss the lower levels."

John almost snorted, but contained it. Sherlock really ought to find a way to put that acting talent to good use. Smith was already grinning.

"Well, I wouldn't want it to be too fun," Smith said. "But I'm glad you enjoy the work."

"I was just looking at Fiendfyre, sir, and remembered hearing that Grindelwald used the threat of Fiendfyre to keep the Wizarding communities in Poland under his thumb. Is that true, sir?"

Sherlock was all wide-eyed interest, actually rising slightly on the balls of his feet as if anticipating the answer. Smith cleared his throat and looked around the room, any direction except at the Ravenclaw who appeared to be hanging on his answer.

"Well," he began slowly. "Do you know, I can't quite recall? I was a bit busy around that time with the troubles in the Muggle world and –" he broke off. "Look, why don't you ask Professor Binns? I'm sure he knows much more about it than I do."

"You were busy?" Sherlock prodded, still leaning forward in studious attention. "But Grindelwald was in power 70 years ago…" his voice trailed off, leaving the question silent.

"I've done a great deal of study on that time period in the Muggle world," Smith said, sounding almost as if reciting a memorized line. "I find the parallels between our world and theirs fascinating. I think you may be right, Sherlock, but you'll need to confirm it with Binns. Let me know, won't you?"

Sherlock came back to the table, scarcely able to contain his grin of delight. Lindsay and John looked at him, waiting for an explanation. He flicked his wand to reinstate _Muffliato _and leaned closer to them under the pretense of reaching for another book.

"We've just made excellent progress."

John looked over at Lindsay, who seemed to have understood. "Sorry? Why is finding out that he doesn't know a bit of Wizarding history 'excellent progess'? Ask any wizard in Hogsmeade, they couldn't tell you what Grindelwald did in Poland."

"No," said Lindsay and Sherlock at the same time. They stared at each other for a long moment, then Lindsay waved him on, leaning slightly back to show he could continue.

"But, a wizard who claims to be an expert on both Defense Against the Dark Arts and that time period in Muggle history would know. Almost assuredly. And Grindelwald never even attacked Poland. He used the threat of Fiendfyre to control the wizards living in the Black Forest because a rampaging forest fire would not only force them out of their homes, but expose them to the Muggle community – simple and effective. It's one of the most commonly cited examples of wizarding warfare. Any competent wizard would know that."

"Since when have we considered Smith a competent wizard?" Lindsay interjected.

"Never, which is surprising, since Minerva McGonagall isn't the type to hire idiots just to have someone fill the job. And I don't think he's unintelligent, just singularly un-gifted with magic. Which begs the question: why is he teaching here?"

"You think he's connected to the attacks."

It was a statement, not a question. John, who had been reaching for _The Dark Forces: A Guide to Self-Protection_, took a moment to try and close the gaps in reasoning.

"He's not a particularly gifted wizard, he doesn't look like most wizards, and he seems to be a bit out of step with the rest of us. He just now seemed to have insinuated that he was alive when Grindelwald was. You think an alien is behind Chimmy's death, and this fellow has all the earmarks of being… not human."

Both Sherlock and Lindsay grinned.

"Precisely," said Sherlock.

"So you're saying Professor Smith might have killed and apparently eaten a house elf?"

"No, I'm saying he might have killed and eaten four house elves."

"Beg your pardon?"

"The note he just received. He had it on his desk, which is why I asked him about Grindelwald in the first place – the handwriting was so slapdash I needed a moment to decipher it. Three elves disappeared from the kitchens this morning. One of the other elves seems to have seen something, but she's currently sedated because she was so traumatize. Thus the fact that McGonagall said Smith didn't need to come right now."

Lindsay leaned back even further, cutting a glance toward the teacher's desk. "That seems like a bit of a leap – from 'he doesn't know History of Magic like he should,' to 'he's an alien elf-eater.'"

"I don't have proof, but it's a theory that covers the facts as we know them. As we gather more facts, we'll know more."

"But that _thing_ had claws and teeth and climbed rafters," John objected, then answered his own thought. "Animagus – or …"

"Some sort of shape shifter, yes," Sherlock said. "I plan to talk to Professor Sinistra by Monday, and until then, I think we should keep a close watch on –"

"I think this will be sufficient," Smith said from directly behind Sherlock. "It doesn't appear that you're getting much more done."

All three of them jumped guiltily.

"Sorry, Professor, we just got distracted," John said, handing him the one parchment he'd filled out since Sherlock took the rest.

"Well, I suppose two hours is sufficient. Now consider yourselves scolded for skipping out on the meeting and letting Peeves in and don't let it happen again. I don't do second chances."

They all smiled and nodded, resisting mightily the urge to glance at one another.

"Alright, then, off you go," he said, making shooing motions.

They all but bolted for the door as he drew his wand and flicked it at the parchment and books. The parchment flew up and wrapped itself around his head, while the books merely flopped a few inches down the table. _Jinxes for the Jinxed _fell off the end just as John closed the door.

"So what do we do?" Lindsay asked as they paused at the turning in the corridor. "Should we talk to Professor McGonagall?"

"Not till we've checked all the variables. It's not airtight yet, but it covers all the evidence we have. So what we need is more evidence. I technically have a way to check immediately, but I'd like to keep my brother out of this if at all possible." Sherlock looked almost conflicted as he said it, but didn't qualify his statement.

The door to Defense Against the Dark Arts classroom opened and Smith strolled out, looking concerned. Almost instinctively, all three ducked around the corner and waited. Rather than turning toward the stairs to the entrance hall that would lead to the kitchens, Smith headed down the corridor of classrooms, hands deep in his pockets and eyes on the ground. He walked past them without noticing their presence and continued to the next corridor turning to the left.

There was no need to ask each other. As soon as Smith had turned the corner, the trio followed. Sherlock dashed ahead and peeked into the corridor.

"He's headed for the Transfiguration study."

"McGonagall's old office?" John whispered.

Sherlock nodded. "He's got a key in his hand."

He looked back at them and grinned. "The game is afoot."


	11. Chapter 10: Of Kitchens and Corridors

"Now explain to me why we're out in the courtyard when it looks like rain instead of waiting for Professor Smith?" John asked as he and Lindsay half-jogged to keep up with Sherlock's darting progress around the yard.

"Because standing at the keyhole when he came out might look a tad suspicious, don't you think?" Sherlock replied, stepping up on a bench to get a view of a large knot of Hufflepuffs playing with a de-fanged Frisbee.

"Fair enough, but I thought we were going to tail him."

"No. What we need right now is Molly."

"Sorry, you mean Molly Hooper?"

John could see him roll his eyes before he even turned around to face them.

"No, Molly the barmaid in the Hogshead. Of course Molly Hooper! Do you see her?"

John stammered out a negative, whipping his head around to look.

"I could send a patronus," Lindsay suggested.

"Not unless you can arrange for it to only deliver the message if she's alone. A patronus would attract too much attention. There aren't many who can cast one," Sherlock said, heading down the hill toward the lake. "Lindsay, you're her homework partner, where would she be on a late Saturday afternoon?"

Lindsay furrowed her brow and stopped walking. John paused as well, clearing his throat so Sherlock would notice. He turned, heaving a sigh of irritation.

"She's not much of an outdoors type," Lindsay began. "With those clouds, I don't think she'd be out here."

"Alright, then, where would she be?"

"I didn't say I knew that," Lindsay retorted. "Just telling you I don't think she'd be here."

"She has a cat," Sherlock said suddenly. "The owlery. Let's go."

They didn't bother asking him to stop and explain, just headed back into the castle on his heels. Sherlock nearly bowled Molly over as they dashed around a turn in the stairs and met her coming down. He grabbed her elbow and turned to face the others before she had completely caught her balance.

"First weekend, little homework, she's a Hufflepuff, she'd write home on a rainy afternoon. She doesn't have her own owl, so she'd have to come up here."

Molly nodded mutely.

"We need to get into the kitchens to talk to the house elves. Can you take us?"

"Well, I – I don't –"

"I know how to get in," John volunteered. "I could have told you that if that's what you were after."

"But do the house elves trust you?" Sherlock asked.

John thought back. He'd started out on pleasant enough terms with them, but he and a contingent of Dumbledore's Army had sneaked in to coat the goblets for certain members of the staff with burning bitterroot powder, and several elves had gotten the stuff on their hands. No amount of apologies from the entire DA had quite made up for the incident.

Sherlock correctly interpreted his silence. "Very well, then. Molly, will you help us? There's been another incident with the elves."

"Another killing?"

"We're not sure, but we need to get in there before anything else can happen. Will you help?"

He was playing her, and well. If there was one thing John already knew about Molly Hooper, it was that she'd do just about anything to keep more harm from befalling helpless creatures. Her nod moments later came as no surprise.

"Tickle the pear? That's it?" Sherlock grumbled as they stepped through the door into the kitchens.

"Shh!" Molly warned, stepping behind a towering pile of potatoes. "If Noby is in charge right now, he'll kick us out. Says students only cause trouble in the kitchens."

John gave a guilty shift. "Besides, surely the professors will have someone down here," he muttered.

"Not necessarily," Sherlock replied, modulating his own tone to a whisper. "It would be just as easy for the house elves to bring the witness to whomever wanted to talk to it as soon as it awoke. Which is why we're down here first."

"But if the house elf is still sedated –" Lindsay began, but Sherlock cut her off with an emphatic motion of his hand.

Several house elves were rushing by with tea trays. Sherlock nodded at Molly, who stepped out to speak to them.

"Good afternoon, Gubby."

"Oh, Molly Hooper!" the one called Gubby exclaimed, nearly dropping the tray from above his head.

Molly steadied it for him while he regained his grip. "Umm… how are things?"

Gubby blinked at her from underneath the tray. "Not good, Molly Hooper. Not good at all. But nothing Gubby can do to help except stay away when he's told."

"Stay away?"

Sherlock stepped out from behind the potatoes, "From where? Where?"

The elf jumped, giving a terrified squeal. Molly grabbed at the tray, but missed. Sherlock shot an arm out and grabbed the teapot as the tray slid backwards and hit the stone floor. Cream spread sluggishly.

John and Lindsay joined the group, stooping with Molly to collect the rolling teacups.

"Where do they want you to stay away from?" Sherlock demanded.

Gubby merely stared at him. Sherlock turned to Molly in abject irritation. She waited till she'd picked up the chipped pieces from a saucer and laid them gently on the tray before speaking again.

"Gubby, we're here to help. We need to know about what happened here today."

Gubby looked at the remnants of the tea service. "Gubby was told not to speak. Professor McGonagall said Gubby was to stay away from the flue and keep Winky comfortable until she is wanting to speak to her."

Sherlock had hopped over the tray and was heading toward the large fireplace before Gubby finished speaking.

"It's okay, Gubby. Thank you," Molly said, patting the elf's shoulder. "Can I help you fix up another tray?"

"Oh no, Molly Hooper. You know Gubby won't let you be helping with his work," Gubby said stoutly. "Gubby will let you and your friends look around as much as you want." He turned to Lindsay and John, who were putting the final broken pieces on the tray, and saw John.

John attempted to smile, but the house elf recoiled instantly and looked up at Molly, ears drooping as though he felt betrayed.

"Molly Hooper has unfortunate friends," Gubby said finally. "But Gubby will let them stay."

Sherlock dashed back from the fireplace. "Did you say you're keeping Winky comfortable till McGonagall has time to talk to her?"

Gubby nodded.

"So she's awake."

"Winky likes her butterbeer, sir," Gubby said. "Madam Pomfrey gave her a potion, but Winky drank a whole butter beer instead. She is sleeping now, and Gubby will tell Professor McGonagall when she wakes, even though it isn't –"

"So we could wake her now," Sherlock interrupted.

"Sherlock," Molly protested faintly.

"There's almost nothing to learn from the flue," Sherlock said. "One of the clawed things came down it, smothered the banked fire, scattered the ash on the floor, and climbed back out the same way. The footprints that might have been there are gone because those elves already swept, but you can see a scattering of ash over to the right. It would have had to have been swept there, likely by the creature's tail. The elves would have cleaned it up if they'd noticed scratch marks are a little closer together than we saw them before, but that's probably due to the fact that a vertical ascent requires more careful navigation than across a rafter. It appears to have been the larger one. Other than that, your busy little friends have obliterated everything."

"Fantastic," John breathed.

"Now," Sherlock said, turning back to Gubby. "Will you take us to Winky?"

"Winky is not wanting to talk to - "

"Never mind, just tell me where she is. I can find my way."

Gubby looked imploringly at Molly, who was avoiding his eyes. Then he sighed and shuffled off to the left, beckoning them to follow. "Winky will be upset, maybe even angry," he warned as they approached a veritable honeycomb of elf cubby holes built into the walls.

Each space was large enough for a comfortable elf nest, with little rungs built into the dividers so the elves with higher accommodations could reach them. There were a number of beds filled, the elves who did the night cleaning, John assumed, and a concert of snores built as they ventured further.

Sherlock had spotted the dark end of a butterbeer bottle sticking out of a middle cubby before Gubby gestured to it, and was already crouching to peer inside.

"Winky," he said firmly. "Wake up."

The little elf opened her tennis-ball-sized eyes blearily and let out a squeak of terror at the group of students clustered around her cubby.

"It's okay, Winky," Molly said soothingly.

She edged around Sherlock to hold out a hand, beckoning Winky to sit up. Sherlock reluctantly gave her a few inches to coax the elf to the edge of the cubby, where she sat weaving slightly and rubbing her bloodshot eyes.

"I need to know exactly what you saw this afternoon," Sherlock rapped out. "As much detail as you recall. Don't leave anything out."

Winky's face collapsed into distressed wrinkles. "It was an evil, evil thing. Winky is lucky to be alive. Winky could have been taken, too."

"Taken?" Lindsay asked.

"Th-the thing came down the chimney and stung three elves while Winky watched."

"Stung?" Sherlock interrupted.

Winky nodded, and winced at the motion. "With its tail. Snap, snap, snap, and they all fell over. It grabbed them and jumped back up the chimney before we could do anything. Winky was just going to build up the fire for cooking when it happened. If Winky had been closer, it would have gotten her, too." A few giant tears splashed down on Winky's blanket.

"When? Specifically."

"Just after lunch. Winky doesn't know what time."

"Has it done this before?"

Winky shook her head, but cautiously.

"Has it been in the kitchens before?"

"W-winky does not know," she said miserably, putting her head in her hands. "Eight elves were attacked before school began, but Winky never saw… that before."

"Did anyone?" Sherlock moved forward, shouldering Molly out of the way. "Another elf we could talk to?"

Winky shrunk back from him, shaking her head so her ears flapped. "It is an evil thing and it hides so no one can see it. Like no magic Winky has ever seen."

"Yes, we assumed that much," Sherlock said, motioning her to continue. "Describe it."

"Winky thought it was a bear," she said, drawing her blanket up to her chin. "It is furry and big and has claws like bears. But its eyes..." Sherlock was on the verge of urging her on when she took up the narrative again. "Big and red, and –" she groped for words. "Like bug eyes."

John half-expected Sherlock to follow up on that description, but he merely nodded. "I understand. What else?"

"It was the color of the fireplace. Winky saw it turn from fire colors to brown while it stung the others."

"Yes, we know about that," Sherlock interrupted. "How many limbs does it have?"

"Limbs?" John repeated.

"It took three house elves and still managed to climb out the chimney. Did they just play piggyback?"

"It has four arms that Winky saw," the elf volunteered, letting the blanket fall back to her lap. "Two legs it stood on, and four for grabbing and climbing. And the tail. An evil, evil creature."

Sherlock nodded and backed away. "That's all we need. We can go now. Professor McGonagall will want to speak with Winky, and it wouldn't do for us to be seen around her."

"Thank you, Winky," Molly said, smiling at her and patting her shoulder. "You were very brave."

Lindsay and John paused to thank the elf as well. Sherlock was already halfway to the entrance by the time they caught up.

"Did you recognize the description?" John asked. "You seemed in an awful hurry to get out of here."

"No, but given the fact that the elves had finished cleaning up from lunch, we can assume the incident happened around 1:30, which means that, allowing for time for messages to be delivered and people to arrive, any tonic Madam Pomfrey would have given a creature that size will be expected to wear off within the next 10 minutes. I felt it best to be gone from the kitchens before we find ourselves surrounded by professors."

Molly stopped outside the door. "I'm going back to my room before dinner."

"Alright," Sherlock said, continuing on without stopping.

"Come along with us," Lindsay invited. "You've been a big help, and I'm sure –"

"This sort of thing isn't really Molly's area," Sherlock interrupted, coming back a few steps.

"Because you know her so well," Lindsay said shortly.

"No, he's right," Molly intervened. "I didn't really want to know as much as I do now, and I'd like to forget it as soon as possible. I'm going to see if I've got any more of the preserved flowers my mum gave me, so I can take one to Winky."

She waved and gave a very noticeable sigh of relief as she turned toward the Hufflepuff dormitory. The three others went the other direction toward the main stairs.

"Where now? To find Professor Sinistra?" Lindsay asked.

"I thought we'd give McGonagall's old study a go."

"What if Smith is still in there?" John protested. "I don't fancy my parents getting a letter from McGonagall because I can't seem to stay out of trouble. They got their share of those last year."

"Smith will be with McGonagall while they talk to Winky, right?" Lindsay answered, quirking an eyebrow at Sherlock to confirm. He nodded and took off up the stairs.

"How many letters?" Lindsay asked John as they jogged behind him.

John's mouth tipped up on the left side. "Six. Yours?"

"It was supposed to be 5, but McGonagall intercepted the last two and burned them. She knows how it is with my parents."

"She slipped a note in with my second one, explaining she supported my actions and the new headmaster was being excessive in implementing his new order. My parents took her word for it."

"Lucky," Lindsay said wistfully. "I got an inquisition with all of mine. And I couldn't tell them or they would have taken me out."

"And then just think how many pranks you never would have been able to pull on the Carrows."

"Just think of how dead you would be, you mean," she shot back, laughing.

"If you two are done reminiscing," Sherlock called impatiently from the landing. "We don't have all day."

They met Smith on the fifth floor. He nodded distractedly and continued on his way toward the gargoyle-guarded entrance to the headmistress' office. Armed with the knowledge he was gone, the trio moved even faster toward the Transfiguration study. Sherlock shook his sleeve down over his hand and tried the knob.

"Didn't really expect it to be unlocked," he muttered as the door refused to yield. He drew his wand and said, "Alohomora!"

The door did not yield. Rather than express frustration, Sherlock grinned.

"I actually thought that might be the only locking spell he'd be capable of producing," he explained to Lindsay and John. "But he has a more powerful spell than that on the door. Impressive."

"Finite incantatem?" Lindsay suggested.

"Most sealing spells don't respond to that if they're properly set," John protested.

"And we're assuming Smith properly set it?"

"Fair enough."

"_Specialis revelio,_" Sherlock said, pointing his wand at the key hole. "Scarpin didn't realize that his Revealer Spell would work on anything, not just potions. It has come in handy…" His voice trailed off as he stared at the door.

A combination lock materialized above the knob with a large circular panel and interlocking circles, each with a unique set of dots, curves, and swirls. They stared at it, perplexed. Sherlock pointed his wand at it, but no spell immediately came to his lips.

"Is this one of those things that Muggleborns missed out on as kids? The magical circular locks?" John asked.

"No," Sherlock said, leaning closer to observe the circles. "It's definitely not of this world."


	12. Chapter 11: Trouble Brewing

"Can you open it?" John asked after Sherlock's silent examination of the lock had stretched to uncomfortable limits.

"The oil deposits are heaviest on this circle and this one," Sherlock said, indicating an outer ring and one just inside it. "Equally heavy, in fact, as if both hands are used to move them simultaneously. Unfortunately, after that, the sequence becomes impossible to detect, and with this circular design, it would take me until tomorrow morning at the earliest to crack it, and I don't think we have that kind of time."

John scratched his head, irritation warring with concern. Out in the stairwell, a peal of laughter and the pounding of shoes announced a group of students heading up, likely to their dormitories. The noises bounced faintly off the stone walls of the corridor, seeming much louder than they were given Sherlock's all consuming concentration.

"You said you had a way to find out about Smith right away," Lindsay said finally. "Don't you think it's time we used that?"

Sherlock's face contorted into an expression rarely seen on faces older than six. "We're not quite so desperate just yet."

"What are we waiting for, then?"

Sherlock turned around and leaned back against the wall, steepling his fingers under his chin. "The creature entered the kitchens through the flue, and exited the same way. No one has seen it do this before, and we've seen its trail to the balistrarias with our own eyes, so it's breaking its routine. Why?"

"It found a quicker way in?" John suggested. "Why bother with all the hallways and people if you can get straight at the elves?"

"Yes, but it's only just now chosen to come in this way. After killing eight others? There's a reason. The flue from the kitchens leads out on the north side of the castle – the side facing the Black Lake. In fact," he stood up straight suddenly. "It should be just round the corner from this room. The windows for this study face the courtyard, don't they? It would be just a short climb from the Astronomy tower."

Before Lindsay or John could comment, Sherlock shook himself. "Listen to me. I'm trying to find facts to fit my theory. Childish. Ought to know better by now. Let's begin again. It's obvious Smith is hiding something in this room, and despite being a fairly spectacularly inept wizard, he's locked it in a way that it presumably only he knows how to open. It's also clear that whatever or whoever the creature is, it's changed its habits of late – it took the elves with it rather than eating them there. Part of it, naturally, is that the return of the students will have made it much harder for it to feed. But the fact that it came in daylight today also seems suggestive."

"Something to do with the Saturday schedule?" Lindsay said.

"Perhaps," Sherlock said, heading back toward the stairs. "Regardless, there's an easier way to check our theory about this room being used."

"Outside?" John asked.

Sherlock turned, actually smiling, "Yes. Shouldn't be too difficult to identify the direction the scratches take once they leave the balistraria."

"You do realize it's about to pour puffskeins out there, don't you?" John protested.

"Afraid of thunderstorms?" Sherlock asked with light mockery, continuing down the stairs.

"No, but I don't fancy scaling a vertical wall in them. You'd be asking for a fall."

"Good thing you've got that custard-spell, then isn't it?"

John set his jaw in irritation. Lindsay shrugged at him.

"It hasn't started raining. Maybe we'll be done before the worst hits."

By the time they reached the doors, they were caught in a stream of wet students coming in from the yard. Lindsay and John only took a couple of steps past the archway when the sting of the wind-driven rain convinced them back into shelter. The flagstone courtyard already had currents flowing toward the openings onto the grassy areas. Even Sherlock only ventured a few steps further before returning to the doorway, hair plastered down on his face. The setback would have been more irritating for all if Sherlock's irritation hadn't been so amusing.

"So we just have to wait for it to end?" he huffed, waving his wand across his robes to dry them.

"Or cast an anti-rain spell strong enough to drive all of this away," Lindsay observed.

Sherlock growled. "I know the theory of meteorological spells, but I've never tried one, and certainly never one of this magnitude."

"That surprises me," John said, chuckling at the glare from under the fringe of hair that Sherlock was in the process of drying. "No, really. I assumed you would be the type to be casting hurricanes in your backyard when you were supposed to be taking an afternoon nap."

"When I could get my hands on a wand at that age, I was more interested in experimenting with transfiguration."

"Of course you were," John sighed. "Well then, no wall climbing for tonight. Any other big ideas? Dinner should be any minute."

"We have homework that ought to be done," Lindsay said reluctantly. "I'm betting that essay for Flitwick isn't going to be something we want to be starting tomorrow night at curfew."

"I was planning on doing that during History of Magic Monday," Sherlock said.

"Yes, but some of us don't write at the speed of light," John countered. "Besides, no one said _you_ had to do homework tonight, just us mortals." He frowned. "Though we still haven't finished the lethifold diagram or the essay."

"You haven't?" Lindsay asked, surprised. "Molly and I had that practically completed by Thursday."

"You have a Hufflepuff partner," John said pointedly. "I don't."

He hadn't meant it as a goad, mainly because he was quite certain such things didn't work on Sherlock Holmes, but the 15-year-old had furrowed his brow at the words. He seemed to be sorting through some unfamiliar information in his head.

"When will you be working on it?" he asked, his words strangely halting.

John shrugged. "Dunno. Probably head to the library after dinner."

Sherlock set his shoulders as though about to face down a harpy. "I'll be there."

All told, it wasn't the least productive night of homework John could remember, but it was certainly stiff competition for the night the Daily Prophet reported Harry Potter had been sighted leading Muggleborns out of the ministry. Sherlock found the lethifold tediously boring, and spent most of the time muttering about alien information and how Professor Sinistra had been absurdly close-minded about the subject when he'd asked her in the Great Hall. John had managed to get a fair chunk of the Charms essay completed, and the lethifold assignment lacked only another foot of parchment. It was with a pleasant glow of purpose that John had headed into the dormitory that night.

He was jolted from a dreamless sleep by a moaning wail. He had one foot on the floor and was kicking the other out of the sheets before he realized that the sound hadn't come from within his room. The interrupted snores around him confirmed he was not the only one to hear it. He nearly tripped over Harold Fortescue, the prefect, in the hallway. Their muttered, confused apologies were interrupted as the sound came again, more like an agonized groan.

"Above," Harold said, heading up the steps.

They met two students coming out of a room, supporting Dean Thomas between them. The boy was bent nearly double, clutching at his side.

"He just started yelling," one said, his face white in Harold's rather shaky wandlight. "He's all clammy, too."

John stepped up to Dean, detaching his grasping fingers from the pajama fabric. There was no bloodstain apparent on the clothes.

"It burns!" Dean gasped out, keeping another moan in his throat with an effort. "Worse than fiendfyre."

"Someone go get Madam Pomfrey and Professor McGonagall," John ordered, easing Dean into a semi-reclining position on the steps. "Go on!"

He jerked Harold's wand closer and moved the shirt up, revealing a small puncture wound just below Dean's right ribs. It was small enough to have been made by a quill, and likely hadn't bled more than a drop, but the heat emanating from the flesh around it was enough to confirm that it was no ordinary injury.

Dean curled into himself again, knocking aside John's probing hands. "Making it worse," he ground out.

"Sorry, mate, but I'm going to have to," John said firmly.

The sound coming from Dean's mouth was half-feral, but John patiently pried his hands away from the injury.

"Trust me, Dean. You're going to be okay. You have my word."

There was little more to be gained from examining the puncture. John took only long enough to realize the wound was almost perfectly round without any tearing at the edges before letting Dean curl up again to wait for Madam Pomfrey. The boy was in enough pain to not mind whimpering like a child in front of his classmates, a rather ominous realization. John settled back on his haunches and looked up at Harold. The boy had been asked to remain outside the doings of the DA the year before, as his position put him at a greater risk of discovery and the younger children still needed a solid leader they could count on. His lack of experience with emergencies showed in every sweat-soaked line of his face.

"Will he be alright?" Harold asked, his voice rasping.

John nodded, not bothering to say anything as Dean shuddered through another groan beside him. He was surprised they didn't have more of an audience, but there were only three doors open, and the boys seemed content to watch from within their rooms rather than come out and help. John was spared having to suppress his annoyance by another scream – this one higher pitched and coming through the wall. He bolted to his feet.

"Stay with Dean," he commanded Harold. "I'll go see."

He'd only made it up three steps of the staircase to the girls' dormitory when his feet flew out from under him and he slid back down the now smooth pathway to the common room floor. He rolled to the side just in time to avoid Lindsay and Hermione as they tumbled to the bottom.

"It's Parvati," Lindsay said as she scrambled to her feet. "I'm going for Madam Pomfrey."

"No need. She's already been called," John said, holding out a hand to Hermione, who ignored it and bounced to her feet, too.

"She's got a small –"

"Puncture-type wound with smooth edges? Says it feels like she's burning up?" John interrupted.

Both girls nodded.

"Who?" Lindsay asked, not bothering to formulate the full sentence.

"Dean Thomas."

The door burst open and Madam Pomfrey swept in, followed by Professor McGonagall.

"Where's Dean?"

John gestured up the stairs to the boys' dormitory. "But Parvati Patil has the same symptoms."

Madam Pomfrey's kindly face settled into an expression John recognized from the battlefield. "Right. Minerva, go with the girls and see to Parvati. I'll be there in just a moment. John, with me."

The light was grey-blue and fuzzy in the windows before they had a chance to stop and regroup. Parvati, Dean, and Robert Cadwallader from Hufflepuff lay in the three beds closest to Madam Pomfrey's study. They were sleeping, but even their sleep was punctuated by little whimpers and catches of breath that said even Madam Pomfrey's strongest pain potions hadn't been quite enough to relieve their symptoms. They'd swabbed the wounds, taken blood for sampling, and spent the rest of the night doing their best to decipher the source.

John had been able to separate a few drops of a foreign liquid from Cadwallader's blood, eliminating the possibility of it being a curse, but the substance proved impossible to identify. He and Madam Pomfrey agreed it wasn't a simple poison, but beyond that they were stymied. Madam Pomfrey poured over her copy of _A Healer's Reference to Poisons and Antidotes _but so far had uncovered nothing that matched these symptoms exactly. John spent half the night sweating over a cauldron in an attempt to separate the components of the stuff, only to find them stubbornly fused. He'd duplicated the sample over and over, setting up more cauldrons for Madam Pomfrey to test, but none of them had been conclusive.

"I'm sending an owl to St. Mungo's," Madam Pomfrey declared finally, collapsing into the chair behind her desk and drawing a roll of parchment from the drawer. "They'll have to send someone down."

John, who had cast Scarpin's Revealer spell for the fifth time, merely nodded grimly. "Did that Burning Bitterroot rub do any good?"

Madam Pomfrey shrugged. "I think they're resting more comfortably. But what does that tell us? Bitterroot has been a balm for inflammation since the dawn of time. There's no guarantee that it's counteracting the poison."

Her quill scratched across the surface of the parchment. John's fingers curled around the page of failed theories they'd been adding to for the last four hours, and only with a mighty effort restrained himself from ripping it to shreds. They would need the information to share with the healers when they came. He contented himself with scourgifying an empty cauldron with a savagery that nearly gouged the side of the vessel.

Hermione and Lindsay had stayed with Professor McGonagall to talk to people who knew Parvati and Dean, hoping to find out a common thread they could use. They'd sent a house elf with a message for Professor Slughorn an hour ago, but he had yet to respond. John was doubtful that the old man would be much more help than Madam Pomfrey, but she was unwilling to give up until she'd exhausted all her resources.

John was still working on the last cauldron when Professor Slughorn entered.

"Sorry to keep you waiting, Poppy," he said gruffly. "I was delayed by one of my NEWT potions students who'd heard the commotion in the corridors and wanted to know if he could help. Now, what have we here?"

John tried to write off the immediate burst of irritation as tiredness, but wasn't very successful. Chances were much better that Slughorn had dozed back off after receiving the message, and that put the portly professor on the same level as whoever or whatever had done this. The fact that Madam Pomfrey accepted his explanation without so much as a questioning look made it even worse. He put his wand away and sat in the chair beside Dean's bed, still for the first time since he'd heard the first scream.

"I can't identify this, Horace," she said, motioning him over to the cauldron that still held the liquid. "It's not just a simple poison, but _specialis revelio _does nothing except swirl it around in circles. And those marks on them – I've never seen the like."

John pictured the marks again – roughly the size of a wand tip, but whatever had made them was razor-sharp. McGonagall had sent a message that nothing that could have caused the wound was found in either dormitory, but that left the whole of the school and grounds as possibilities. None of the victims seemed to have known they'd been hurt, so it was likely something they would brush off – like an ant bite or…

The pieces fell into place. They had been nagging at him throughout the night, but pushed aside in favor of the immediate need for potions or information or bandages.

"Could it be a venom?" he asked, interrupting Slughorn's examination of the cauldron.

Slughorn looked at Madam Pomfrey, who shook her head. "I thought the same, but there aren't any poisonous creatures with only one fang, or a stinger that large. I even tested it for Garuda venom, but it was inconclusive."

"But if there was such a creature, one that could make that kind of puncture mark?" John persisted, getting up from his chair.

Slughorn gave a kindly smile. "Yes, but if we were to base identification on the chance that such a creature might exist, we'd be no closer to a diagnosis, now would we?"

John ignored the condescending tone. "I need to go check something."

"Not likely, young man," Madam Pomfrey said, eyeing him shrewdly. "You're exhausted. You're not supposed to be exerting yourself, and here I've kept you up all night with me. You're going to have a lie-down."

"I'm not exhausted," John protested, voice rising. "I'm 17, for Merlin's sake, not 107."

"What is your idea?" Madam Pomfrey asked, voice softening ever so slightly.

"I – I can't explain it properly," John said helplessly. "But I think I can. I just need to go find someone." He snatched up the roll of parchment from Madam Pomfrey's desk.

"I can go post this for you, and check on my way back. It won't take long, I swear."

Madam Pomfrey met his eyes, and he read the concern there with no small amount of frustration. She still saw the stack of potions bottles and the cane, even though he'd stopped using the lot. In her eyes, he was nearly still a patient. He set his jaw and waited.

"Get on with you, then," she said finally. "But come back as quickly as you can with whatever information you get. I'll want to keep you around till this is settled."


	13. Chapter 12: The Waiting Game

John nearly threw the post owl out the owlery window in his haste to get to the Ravenclaw common room. Never mind the fact he didn't know the password, John was prepared to hammer on the door until Flitwick himself came to ask what was the matter. He'd just rounded the corner onto the correct corridor when he saw a boy ahead in a blue-trimmed robe. The Ravenclaw turned at the sound of his footsteps, and John recognized Victor Trevor, the boy who had done the potions work for Sherlock.

"Oh, you're –ah, Holmes' homework partner, aren't you?" Victor said, smiling at him. "You're up early."

"You, too," John said, returning the smile instinctively, though his mind was hardly processing his words.

"I rather foolishly set three potions to mature in the laboratory Friday evening late – they needed two counterclockwise stirs and some ginger root at 6 a.m. and now I'm heading back to bed."

He was fairly certain he shared the laugh with the boy, but he was more focused on catching up to him than anything else. "Listen, I need to see Sherlock – any chance I could come in with you?"

Victor hesitated. "It's a bit early, don't you think? I've seen Sherlock when he first gets up, he's no morning glory. I think the last time someone woke him before he was ready, the kid ended up turning in his final potions essay in Gobbledegook."

"I'll risk it."

Victor looked him up and down. "Something wrong?"

"No, just –" John cast about. "Homework."

They reached the arched doorway, but rather than speaking a password, Victor simply knocked on the eagle doorknocker. The bird's beak opened, and a woman's voice spoke.

"Does the wizard learn from his wand, or the wand from the wizard?"

Victor frowned. "I hate wandlore. Stuff and nonsense if you ask me. But I don't think that's the answer she's looking for."

"You mean there's not just a password?" John asked, looking back down the hallway toward the stairs. He would have to hurry or Madam Pomfrey would waste time and energy worrying about him rather than the patients who needed it.

"No. Daily riddles, courtesy of Rowena Ravenclaw," Victor said, passing a hand down his face wearily. "Should have just let the potions spoil."

He though a moment longer. "They – they both grow together… like stem and root."

"Insightful," said the voice, and the door swung open.

Victor gave a sigh of relief and dashed through. "I can still get another couple of hours of sleep before breakfast ends. Nice seeing you, er –"

"John."

"Right. John. Well, have a good day, John. I'm off."

"Wait!" John said, moving forward despite staring around at the pristine room that bore little resemblance to the Gryffindor common room. There were far too many breakable things for his comfort. "Which room is Sherlock in?"

Victor pointed to a sofa that had been dragged out of alignment with the others and was positioned facing a window. "He usually drops off there."

Sure enough, Sherlock was sprawled across the blue velvet cushions, a book dropped against his left cheek and a roll of parchment tucked under his right arm.

"Sherlock?"

The boy sat up so fast the parchment ripped and the book toppled to the floor. "What? What's – I'm – oh, John!" He pulled a slim volume from underneath him, wincing. "Terrible sleeping plan. Books on the floor from now on. What happened?"

"Sorry?" John said, his brain still separating the string of words.

"You're in the Ravenclaw common room – traditionally not a place one would find a Gryffindor at this hour of the morning. It's not NEWT arithmancy, John. What happened?" Sherlock got up, whipping his tie from his neck and tucking it into a robe pocket.

"Poisonings. Three of them so far. They've got round puncture marks on them – not all in the same spots – and they feel like they're burning up from the inside."

"House?"

"Two Gryffindors and a Hufflepuff."

"Year?"

"Seventh years so far."

"Gender?"

"Two boys and a girl."

Sherlock frowned.

"Do you think it's the monster-thing? Didn't Winky say it had a stinger?"

"Could be," Sherlock said, turning on his heel and heading for the door. "No way to know until we can compare –"

He turned just as fast, striding toward the stairs to the dormitory. "I need to get Victor."

John filled both Ravenclaws in on the situation on their way back to the hospital wing, over Victor's sleepy grumblings. He wasn't sure about letting Victor in on the situation, but it given that he was the only person who both knew about the samples from the monster and had the potions expertise required to compare the two, it seemed inevitable. Lindsay was waiting outside the hospital wing, and the foursome entered together.

A fourth bed was occupied, a boy writhing under the sheets. A green-trimmed robe was flung across the chair by his side. Madam Pomfrey was hurrying over with a jar of bitterroot paste.

"What did you learn?" she asked, taking in the three other students with barely a blink.

"Nothing yet," John said, pushing Victor forward. "But he's got a... a sample from a creature…"

"A creature I found at the edge of the forest," Victor said smoothly. "It was dead, decomposing, and I'd never seen a body like it. I took some DNA samples and I've been trying to use my potions to discover what it is. John thought there might be a connection between my experiments and the poisionings."

"Do you still have a sample?"

Victor nodded and walked toward the cauldrons still set up in the corner. "May I?"

Madam Pomfrey nodded. "Professor Slughorn went back to his study to look for another poisons book after Noble was brought up. You can work with him when he gets back. John, it's time to reapply the salve." She glanced at the other two. "What can you do to make yourselves useful? If the answer is 'I don't know,' leave now. We don't need more people taking up space."

"Sherlock can work with me," Victor said, motioning the boy over. "He knows my methods."

"I can do anything you need," Lindsay said quickly. "I'm good with potions, or I can help with the salves, or –"

The Slytherin boy moaned loadly.

"John?" Madam Pomfrey asked distractedly, leaning over the boy.

"Lindsay can help me."

He took the jar of salve from Madam Pomfrey and nodded Lindsay to the Slytherin's other side, grasping the boy's upper arm to hold him steady.

"It's Mitch!"

It took Lindsay's exclamation for John to recognize the blonde boy, who had spent half the year working with the DA. His inside information on the workings of Slytherin House had been invaluable, until Amycus found out who was behind the leak and had beaten the boy to the point that Madam Pomfrey had stepped in to stop him. After the boy recovered, Neville had actually ordered him to stay away. He still sported scars just below his left eye and across the bridge of his nose. It had been over seven months since John had seen the boy face to face, and the interim had wrought what seemed to be a decade of maturity in his features.

"Hold him steady, the mark is here on his shoulder," Madam Pomfrey snapped, holding a dropper with the cleansing flush they'd been using on the wounds.

They held him down as Madam Pomfrey dropped the solution into the wound and covered it with a bandage. Mitch let out a choking scream and lashed out. John leaned away to avoid the flailing fist.

"It's alright. It will help, I swear. You're going to be fine." There was no sign that the words had registered at all, but it made him feel better to say them.

Madam Pomfrey's face was drawn as she stood back. "You sent the owl?"

"Yes."

"The others are resting more comfortably. It might be something that will pass, or it might just be getting worse." She tucked an errant grey strand of hair behind her ear and straightened her shoulders. "Give him the sleeping draught and then apply the bitterroot salve to all four. I'm going to try and find bag of powdered valerian so I can make more if we need."

The Draught of Living Death was already on the table beside Mitch's bed. It was the only one that had been strong enough to work on the others. John poured a measure and dribbled it into Mitch's mouth gently. The effect was almost instantaneous. The tight muscles relaxed and the boy's eyes slid shut.

"Well, that's one step sorted," John muttered, feeling his own shoulder relax slightly.

Lindsay stepped over to Parvati. "Do you remember when we had that scrofungulus breakout in the DA last year?"

John unwrapped the bandage around Robert's forearm and gave a hoarse chuckle. "Merlin, yes. I don't think I got a full night's sleep for a fortnight."

"You looked like you'd been trampled by thestrals. That may have been the first time I realized you weren't just a ladykiller."

"Oh?"

Lindsay grinned at him before returning her attention to unwrapping Parvati's bandage. "Let's just say that all I knew of you prior to that was what I heard before stuffing a pillow over my head in the dormitory at night."

"It's not my fault if girls want to talk about me. I've never done a thing to encourage it." John took a large dollop of the orange salve and passed the jar to Lindsay. "Put a thick enough layer that it stands up off the puncture at least a quarter inch. Don't be afraid to press it in a bit, either. Be sure you cover it with the bandage, or it'll just soak into the sheet instead."

Lindsay nodded. They worked in silence for a few moments.

"As I recall, you were one of the last to come down with it," John commented. "One of the worst cases, too. I thought your face might explode."

"If one must be sick, it is better to be spectacularly sick," Lindsay retorted.

"Less talk, more work," Madam Pomfrey interrupted, bustling past with a small burlap sack. "You can see if those two need any help with the potions. If not, I've got some linens here that need washing."

"She doesn't let the house elves touch the hospital wing linens if it's something that can be transmitted to them," John explained in an undertone. "They're immune to most common Wizarding diseases, but she once lost four elves to an outbreak of dragon pox."

They had both been in the Wizarding community long enough to realize how rare this type of concern was. There were few things that had boosted John's opinion of the school nurse quite like that knowledge. He acknowledged Lindsay's surprise with a nod and turned to the two Ravenclaws.

"Anything we can do?"

"Yes, stay away." Victor said, his tone so preoccupied it was hardly even harsh.

"This new case – the Slytherin," Sherlock said, peering into his cauldron. "Is he also a seventh year?"

"No. Sixth."

"So we can rule age out as a factor. And the only house not affected thus far is Ravenclaw. Interesting."

"Yes," Victor said, casting a glance over at Madam Pomfrey, who was setting up a mortar and pestle at the other end of the ward. "Most interesting."

Sherlock looked up at him. "Significant?"

"I think that's more for you to say."

All three of them looked their puzzlement. Victor rolled his eyes.

"I may not be quite so quick as you, Holmes, but I'm in Ravenclaw for a reason. This stuff gives every indication of matching that sample you gave me – though I won't know for sure till I let these potions brew. It's apparent that the two things are linked, and now I find that the only house to remain unscathed is your house."

"Yours, too," Sherlock said, his voice calm and quiet. "What are you suggesting?"

"I'm just wondering if you don't have something you need to tell. Some experiment of yours that seems to have gotten out of your control," Victor said, his voice nearly paternal. "I wouldn't dream of saying it was intentional."

"Don't be a lobalug, Trevor," Sherlock said impatiently. "I have nothing to do with this."

"Then I don't see any other explanation."

The Ravenclaws glared at each other for several moments.

"There's work to be done," Madam Pomfrey called. "Have you found anything out?"

Victor turned to face her. "Only what we had assumed – it's a delayed reaction. They were probably stung mid-day, or late evening in the Slytherin's case. Whatever this is, its purpose is to make the victim suffer – for a long while. It doesn't react like any creature venom I've encountered before, but it does seem to be connected to the samples I took."

"Can we go find the body?" she asked.

"I went back the next day to get more tissues, and it was gone. I assumed the thestrals ate it or Hagrid had buried it," Victor said.

John couldn't help but admire his smooth lying skills, even as he distrusted them. Then again, most of the Ravenclaws he knew had that ability to bluff their way out of anything. It had held Michael Corner in good stead during his many escapades for the DA the year before.

"Well, then, the rest of you make yourselves useful. We won't solve this waiting for a potion to boil."

Several hours later, Charles Boot from Ravenclaw and Dennis Creevey from Gryffindor were also brought in. It was late afternoon when the owl returned from St. Mungo's, saying they would send a healer the next day. An outbreak of spattergroit was stretching their resources thin. They suggested Madam Pomfrey keep the children comfortable, and come by apparition to fetch someone if anyone took a turn for the worse. Madam Pomfrey had nodded grimly and forced them to leave the hospital wing to get some rest and food, promising to call John back if a need arose.

Victor bade them farewell and returned to Ravenclaw tower before dinner. The other three trooped into the Great Hall and sat at the far end of the Gryffindor table. None of them had much appetite, John and Lindsay due to concern, Sherlock due to preoccupation.

"How on earth did the creature get at them all? And at such different times? Charles and Dennis would have been in their dormitories, or common rooms at least," he mused. "It doesn't make any sense. You can't apparate in the school. How is it getting in and out of the castle so easily? And in so many places?"

"I don't know," John said wearily, staring at the roll in his hand rather than eating it. "And going over it again isn't likely to help."

"We need to get into that study," Sherlock said.

Lindsay and John blinked at each other, then at him.

"You said you can't open the lock," Lindsay reminded him "Shouldn't we be looking for wherever the creature is hiding? I think we should look in the forest before it gets dark."

"The key lies here in the castle, though. I'm sure of it. Those poisonings this morning convinced me."

"So you think the creature is somehow connected to the Transfiguration study. It still doesn't fix the problem that we can't get in."

Sherlock smiled. "But if the creature can use an alternative means, so can we."

They waited until twilight, when most of the students were returning to their dormitories or the library to do the homework they'd put off till then. The courtyard was completely deserted when they crept along the wall till they stood beneath the Transfiguration study window.

"And you're sure the window isn't magically sealed?" John asked as Sherlock drew his wand.

The boy didn't bother to reply, just twirled the wand like a lasso till it released a shining magic rope that soared upwards and seemed to plaster itself onto the window ledge. "No better time to find out."

"You've used this spell before? You're sure that rope will bear weight?"

Sherlock rolled his eyes. "When I want to be smothered, I go home. Stop playing Mummy and help me test it."

Sherlock leaned back on the rope, but it didn't budge. With a smirk at John, he put a foot up on the wall.

"I'll go tell you what I see."

"Not bloody likely," Lindsay exclaimed a split second ahead of John.

"We'll all be up there," John said firmly, "Or none of us."

Sherlock rolled his eyes and started to climb. John cast impervioscurrsus on an area wide enough to cover any direction he might fall, but the boy was a natural climber, scaling up the wall in record time. He seated himself on the window ledge and gave a smirking wave down to them before peering inside.

Even from below they could see his start of surprise. He tried the window, but from the rattling, it seemed to be locked. A few seconds and a spurt of wand light later, it was open. Sherlock swung his legs through and called down to them in a hoarse whisper.

"Get up here as quick as you can."

"Dangerous?" John asked, letting Lindsay grab the rope, but keeping her from starting her ascent.

"Not sure," Sherlock said finally. "It's some sort of blue box."


	14. Chapter 13: Answers and Questions

"Have you ever seen anything like this?" John asked the room at large, staring at the blue box dominating the Transfiguration study. If an inkwell or tapestry were to reply, it would merely fit the surreal feeling of the moment.

Sherlock shook his head, but Lindsay nodded. "In an old photo from when my mum was a baby. I think it's like an emergency phone line to the police station."

"So why is a Muggle police call box sitting in Professor McGonagall's old study?" Sherlock muttered, walking around it rapidly.

"New decorating scheme?" Lindsay suggested.

Sherlock paused long enough to roll his eyes and she and John chuckled. John could only muster the smallest amount of repentance as he cleared his throat and settled his face into serious lines. It was possible that he should have taken Madam Pomfrey's advice and napped when he had the chance, as everything was taking on an absurdist hue.

Sherlock stopped at the front door again and pointed his wand at the door, muttering incantations faster than John cared to try to comprehend.

"Any of those circle locks hidden somewhere?" he suggested after several moments of silence.

"No, tried that." Sherlock said shortly.

He stepped back and glared at the door. Then, with a sigh of resignation, he touched his wandtip to the small lock and pressed. A semi-solid silvery substance oozed out, filling the lock.

"It will conform to the grooves used by the key," he said as the other two leaned closer to investigate.

"So there's a spell that turns your wand into a key? Why don't wizards just use that to get past locked doors?" John asked.

"Because it's not exactly in the ministry approved spell books," Sherlock replied, focusing on easing the wand into a counterclockwise turn. "I needed a way to circumvent some specific security measures in my house."

"Where do you live? Buckingham Palace?" Lindsay asked.

Sherlock rolled his eyes. "Buckingham Palace is almost unprotected against magical attack. No, I just have relatives who like to keep secrets."

He turned the wand a bit more. There was a snap and his wand tip separated from the lock, leaving the key portion still inside. Sherlock looked murder at the door.

"The tumblers broke it."

"So give it another go," John suggested, rolling his neck and wincing at the rapid-fire crackling.

"It's not supposed to do that," Sherlock said, sounding both annoyed and slightly lost. "It's not fully solid – it shouldn't break, that's the point of the spell. Which means this thing is actively protecting itself."

He squeezed his eyes shut, brow furrowing, and went completely still. It was an expression John already recognized as one that boded ill for anyone attempting to break his concentration. He looked over at Lindsay, who was walking around the box with a look of utter fascination.

"It doesn't even look weathered," she commented.

Sherlock half-snarled at the noise, but didn't open his eyes. John put a finger to his lips and came to join her at the far corner from where Sherlock stood.

"Magical restoration, I expect. Or a replica," John muttered.

Lindsay nodded, pitching her voice lower. "Though that still begs the question' why'."

Sherlock let out an exclamation that might have been an oath, but the gravel of frustration made it difficult to tell. He opened his eyes to the two of them staring at him.

"Nothing for it," he said finally. "I don't have enough information to eliminate any more variables."

He turned on his heel and stalked to the fireplace. John looked over at Lindsay.

"Did that make sense to you?"

"The sentence did," Lindsay said. "But that –" she nodded to Sherlock, who stood by the hearth with wand half-raised and a deep frown. "That's a puzzler."

Sherlock pointed his wand at the logs beside the fire and levitated several into the fireplace before shooting two flames into their midst. He reached up and took a handful of Floo Powder from the niche built into the mantle and weighed it in his hand for a moment, before casting it into the flames and growling, "Ministry of Magic, Office of Internal Affairs."

He knelt and stuck his head into the green flames, giving one impatient gesture that the other two should follow. They did so, experiencing the odd roller-coaster sensation of Floo Powder travel, though their bodies remained firmly on the stone hearth of the study. The room they peered into was an old, plain office, with a wall of side-to-side filing cabinets and a dusty portrait of Merlin as the only ornamentation.

"Sherlock!"

The reprimand made Lindsay and John jump back at Hogwarts. Sherlock merely smirked. The man who was seated at the desk to the left of the fireplace came around so he could see them, but did not crouch to speak face to face. John started again as he recognized the man with the umbrella who had accosted him what felt like a lifetime ago. He elbowed Sherlock in the ribs, but the boy ignored him.

"Evening, brother."

John whipped his head around to face Sherlock.

"Brother?"

"Yes, 'brother', you heard me," Sherlock said impatiently. "This is my brother, Mycroft Holmes – but I understood you two had already met."

"Informally," Mycroft said, smiling genially.

"What the bloody blazes was all that about, then?" John asked, tempted to climb through the fire and ask the question where he didn't have to crane his neck to see the man's face.

Mycroft shrugged. "Standard procedure."

John mouthed the words back at him, too flabbergasted to even gather words to reply. Mycroft raised his eyebrows and turned back to Sherlock.

"And who else have you dragged into whatever scheme it is you're hatching?" he asked.

"I think the correct appellation would be the scheme _you're_ hatching, Mycroft," Sherlock said sharply. "Tell me what's going on."

"You'll have to be more specific," Mycroft said. "I have at least four matters of international import on my desk at this moment, another half dozen or so of internal affairs investigations, and no small number of everyday chores."

"The giant blue Muggle artifact in the Transfiguration study for starters. Or maybe the new professor who isn't actually a wizard. Or the alien that seems to be developing a taste for magical creatures of all varieties – even human." Sherlock paused long enough for Mycroft to put up a blandly smiling mask. "Whichever you'd prefer to start with is fine."

"What makes you think I know anything about any of these events?"

"Because you know to give the Minister of Magic a hankie _before _he sneezes."

"I am hundreds of miles away –"

"And you know when I've gotten detention before my head of house finds out, so don't tell me you don't know about to daily goings-on at Hogwarts."

"Yes, by the way, congratulations on a full week back with no major incidents. John's doing, I expect," Mycroft said, examining the length of his wand in apparent boredom.

Sherlock rolled his eyes. "Redirection hasn't worked on me since I was 3, Mycroft. Let's start with the alien. It is an alien, isn't it?"

Mycroft pursed his lips, but seemed to resign himself. "Yes. At least, that's the current theory. There has been no indication that it could be anything else."

Sherlock looked near giddy. "Excellent! So why aren't the grounds crawling with Ministry agents trying to find the thing?"

"We were trying to keep a low profile."

"Six students have been poisoned," Lindsay snapped. "I think that might warrant a mention or two in the Daily Prophet."

"We have someone on location who was supposed to keep such incidents from occurring."

"Smith," Sherlock said immediately.

Mycroft curled his lip slightly, but didn't deny it. "He's something of an expert in extraterrestrials."

"Did you find him or did he suggest the posting to you?"

"I've known of him for several years now. When I heard of the trouble, I sent him a message."

Sherlock frowned at the news. "Where did you send the message?"

"I don't know," Mycroft said impatiently. "The Department of Mysteries has some sort of connection with his spacecraft. I conveyed my request to an Unspeakable, and he got the message to the – Smith."

"So he might have already been in the area."

"It's possible." Mycroft crouched to study his brother's face. "Why?"

"Because the only being exhibiting extraterrestrial-type behavior in this castle is your inspector. Are you certain he isn't the one causing the mayhem instead of curing it?"

The eyeroll from Mycroft was almost eerily familiar. John repressed a shudder at the idea that there were actually two Holmes walking the earth.

"Quite certain," Mycroft said, standing back up. "We are receiving hourly reports from multiple members of the Hogwarts staff. I suggest you allow those who are qualified to deal with this and keep your mind on those NEWT classes you're being allowed to take."

Sherlock cocked an eyebrow speculatively. "And if I refuse? You'll have me bumped back to the fifth year classes? Hardly one of your better threats, brother."

"If you refuse, you'll likely get yourself killed," Mycroft said baldly. For a blink of an eye, actual concern crumpled his features. Then it was gone, covered with a flippant, "And don't pretend that being back with your level in every class is anything less than a terrifying thought."

He stepped back, straightening his back and giving each of them a stern look down the bridge of his nose. "Well, this has been a most interesting chat. But I have work to do, and you three should probably get out of wherever you are that you shouldn't be. Good evening Sherlock, Mr. Watson – and Miss Lovejoy, isn't it?"

He flicked his wand at them and the connection was broken. Several seconds later they were reunited with their bodies in the Transfiguration study. Sherlock scrambled to his feet instantly, whirling around to face the police call box again.

"Insufferable," he muttered.

"How did he know my name?" Lindsay asked. "You never told him."

"He's Mycroft, he's known who you were since the moment we were introduced, I expect, possibly sooner. Information is his specialty." Sherlock said, dismissing the question with a shrug. "We're still no closer to understanding what this is."

He walked around it once more, muttering to himself. John heaved a sigh and rolled up his sleeves, positioning himself in front of the door.

"Out of the way, Sherlock," he commanded as the Ravenclaw came around the corner, eyes unfocused.

"What?"

Sherlock stepped back just in time to avoid John's charge at the door. The blue box shook a bit with the force of his body slamming into it, but the door remained solid. John staggered back a few paces, forcing his vision to stay steady by sheer willpower. He had remembered a moment too late that the lack of pain from his shoulder wound did not necessarily indicate a complete recovery. The reverberating pain waves left him momentarily incapable of speech.

Lindsay had seen. "I can have a go at it," she said, edging him to the side as she positioned herself.

"No, I'll be fine," John protested, drawing in a long breath through his teeth.

She'd already thrown herself at the door before he'd finished. The door gave a squeak, but did not yield. She was recovering her balance when it opened from within. Smith, his hair even wilder than usual, looked out.

"Who is it? Oh!" He grinned at them. "I thought I'd be seeing you three."


	15. Chapter 15

John instinctively moved between Smith and the other two. The man gave every indication of being less-than-balanced at the moment, from the wide-eyed, unblinking stare he was giving them to the fact that the robe over his suit was actually inside out.

"Have you discovered where its nest is on the grounds?" Sherlock asked.

John blinked and turned to face him, hoping his expression conveyed his confusion.

"That's where he's been all day. Don't be dense," Sherlock said impatiently. "If the dirt on his instep wasn't proof enough, ask yourself where else he could have been that they wouldn't have had him cooped up in the hospital wing trying to cure all those patients."

"But, Sherlock –" he wished his mind would stop hiding the words he was reaching. "The claw marks."

"They didn't lead to this window," Sherlock said, shrugging. "I assumed you'd noticed when you came up."

John shook his head rather hopelessly. "So he's not –" he turned back to Smith. "You're not the alien?"

"Well," Smith said, cocking his head slightly. "Technically, yes, but if you're asking if I'm the one who has been attacking elves and students, then no."

"Why should we believe you?" John asked.

"Because –" Smith scratched his head. "Because the claw marks didn't come here. Whatever that means."

"But that was only one –"

"It invalidates our theory," Sherlock interrupted. "Remember – theories to suit facts, not the other way around. No claw marks, Mycroft's insistence that there arerecords of this fellow, and obviously not as a voracious carnivore, not to mention the fact that this creature is clearly more adept at concealment than our Professor Smith –"

"Oi!" Smith said, affronted.

"Please. You're blatantly not a wizard, with an alias so ubiquitous and a wardrobe so eccentric you should be at a casting call for some Muggle science fiction show. I was willing to overlook all that while I thought you were merely a beast unable to control his appetite, but these poisonings aren't for food. The creature wants something else, making it sentient and clever, meaning its concealment tactics in any form would be equally clever. Therefore, we can go forward on the hypothesis that you are not the monster attacking the school."

"That's bloody magnificent," Smith said, staring at Sherlock as if he were a new species to be examined. "And only 15? Wonder what you'll be when you're fully grown. Of course, you did just manage to insult me at least twice while proving my innocence, but part and parcel, I suppose. I was out in the grounds, though in my defense I stopped by the hospital wing around dawn to take a lok at the poison-venom-stuff. I'm not exactly certain what it is. Though it would clear everything right up, but it didn't. I don't suppose you three know much about alien subspecies?"

John and Lindsay immediately shook their heads. Sherlock seemed to force himself to do the same.

"Either the TARDIS is malfunctioning or we're dealing with something I've never encountered before. Everything pointed to Zhacan, too…"

"Zhacan?" Sherlock repeated.

"Fairly peaceful race over all, but with a taste for exotic food. It explains the centaurs and the thestrals and the house elves and the reason no humans were harmed up until now. They don't like human. Too gamey."

John found himself wishing a tapestry or an inkwell would intervene to interpret this information for him. "But it isn't a Zhac- thing."

"Can't tell. The TARDIS is having trouble searching our archives. The sonic screwdriver is on the fritz, too. Probably because of the magic in the air. She doesn't care for it much. She's a scientist at heart."

"Who is?" Lindsay asked.

Smith grinned. "The TARDIS. My spaceship." He patted the doorframe of the blue box with almost paternal pride. "Best to be had by any species in this galaxy or any."

"A Muggle police call box?" Sherlock said skeptically. "Bit cramped, it seems to me."

"Let me show you."

He stepped aside with a flourish and beckoned them inside. Lindsay was through the doorway before John had collected himself enough to stop her. Sherlock swept Smith with one more appraising glance and nodded John through the door. With a hesitation only long enough to see that Sherlock intended to follow, John stepped through.

Whatever he'd been expecting to find, this certainly wasn't it. The room was easily larger than the Transfiguration study, full of warm and odd-coloured light, with metallic walls and some sort of console in the center. Lindsay was standing stock still, eyes as big as saucers, but with a grin spreading across her fact that threatened to explode off it.

"Breathe, Lovejoy," John commented as Sherlock stepped through behind him and Smith followed.

"It's brilliant! Absolutely brilliant," she said, dashing several feet forward. "A real spaceship at Hogwarts – and it looks like a phone box? Great Scot, that's amazing!"

"Now she knows how to appreciate the TARDIS," Smith said, shoving his hands in his pockets to watch Lindsay's exploration. "You two are inexplicably unimpressed."

"It's –well, it's impressive," John said, unfolding his arms and taking a few steps further in. "A bit out of the everyday."

Smith rolled his eyes and mimicked him. "'A bit out of the everyday – that's the understatement of the year. At least, I think so. As far as I remember for 1998. When have you seen anything like it? This is Gallifreyan technology at its peak. Its bigger on the inside!"

"It's dimensionally transcendent," Sherlock said in a bored voice. "It exists on two planes. The entry, in the dimension we live in and experience it, is compact and therefore easily concealable and maneuverable. The interior is on a separate plane, allowing for almost unlimited space. It's the same basic theory as an undetectable extension charm, except I imagine your technology aids with transport through space rather than merely increasing capacity."

"And time," Smith said, almost defensively. "Space and time."

"Time?" Lindsay echoed from the console. "It's a time machine, too?"

"Wizards have that ability, too," Sherlock said airily. "Its use is discouraged because it can have rather disastrous consequences."

"That's because you're not time lords," Smith said.

"Time lords?" Sherlock repeated, raising an eyebrow. "Bit of a presumptuous title, don't you think?"

"It's not my title, it's my race." Smith looked at him almost sternly. "My title is 'Doctor,' and as long as it's just us four, you can call me that."

"Like a medical doctor?" John asked.

"Not exactly," the Doctor said, shrugging. "But my knowledge of alien species is unparalleled in this universe, and I can't seem to identify this."

He took the steps up to the console three at a time and pulled the screen around to face them. The tangle of circles and dots was familiar, but no more comprehensible than it ever had been. Sherlock vaulted the handrail to stand beside the Doctor. John considered protesting that he couldn't possibly read it, no matter how close he was, but decided against it. For all he knew, Sherlock could have read up on Circular Alien Languages of the Galaxy last night and now could read it. For his own part, he chose to take the steps one at a time and arrived just as Lindsay bounded past from the other side of the console.

"See? Everything fits with the Zhacan, but their stinger only has a mild paralytic. It just makes a human's limbs heavy, doesn't even completely stop them," the Doctor was saying. "This poison – the composition seems similar, but it must have mutated."

"Are there any species you know of with a venom that doesn't kill?" Sherlock asked. "All six of the victims are still alive, which makes it more and more apparent that killing them wasn't the objective."

The Doctor tapped around the screen several times, and the circles and dots dissolved into a swirling mass. John sighed and leaned back against the console, feeling the tiredness settle on his shoulders again. He was rewarded with a squawk from the machine behind him. He jolted upright and turned around, scrabbling for whatever he'd bumped out of place. He pulled a knob back slightly, and was greeted by a rusty sounding grinding sound.

"You could keep it down, you know," he muttered, putting the knob back in its original position.

"I can get that for you, John," the Doctor said, stepping around Sherlock to pull a lever about a half inch down. "She can be a bit cantankerous about strangers touching her."

"Um… Doctor, is there a way to see this in – English?" Lindsay said hesitantly, eyes still on the swirling monitor. "I realize this is your language, but we can't read it."

"Oh! Right you are." The Doctor turned a knob on the console and the display reformed into letters.

At the top was Zhacan, with a list of attributes and physical features. Just under it was Vhrexing, and then Blagian. John, standing well away from any surface that might protest his presence, squinted at the screen. They all had the climbing ability and claw type of the creature at Hogwarts. Zhacan was the only one with the chameleon-like ability. But none of them had a venom stronger than the Zhacan.

"I can't think of a species that causes that level of pain in a human without killing them," the Doctor said.

"Unless you count humans," John said, his mind flashing to the Death Eaters' vicious attacks, and Neville's face when the older boy had confided in him about his parents.

Both Lindsay and the Doctor looked at him with something akin to pained understanding. Sherlock was functionally ignoring him, eyes still glued to the screen.

"Here," he said, tapping at an entry. "The Waichux has venom meant to incapacitate its victims so it can eat them while they're still alive."

"Charming," John muttered.

"Yes, but the Waichux never travel outside of their system. And they're basically giant transparent slug-creatures, so I don't think the Zhacan would have crossed with them."

John repressed a shudder and decided to risk letting the handrail take his weight. It was going to be a long night.

Three hours later, they were no closer to having an exact match, and the Doctor and Sherlock looked as if they'd been in a boxing match. Sherlock's tie hung askew from his neck and he'd tossed his outer robe in favor of rolled shirt-sleeves. The Doctor's hair was now in some sort of fantastical arrangement that reminded John of the stalagmites he'd seen in a cave on holiday once. Lindsay had found a perch in the branch of one of the oddly angular columns and was chiming in with suggestions when the other two stopped for breath. John had stopped contributing over an hour previous and contented himself with pacing halfway around the console and back again, keeping himself awake and still seemingly engaged. It occurred to him now that they were being exceptionally quiet. He rounded the turn once more and found all three rather wilted.

"Listen," he said, his voice raspy with weariness. "Can't we just go out at first light and look for the blasted thing?"

"I spent the whole day out there today and only managed to get myself royally lost," the Doctor said.

"That's because you don't know the forest."

At that, Lindsay sat up straight, eyes gleaming. John nodded in answer.

"John and I do," she said. "We went out there regularly last year. We could help you search."

The Doctor tilted his chin up to think. "Aren't students banned from the forest?"

John gave a laugh. "Never stopped us before."

"Well, it can't be at first light. I've got a meeting with Headmistress McGonagall and Madam Pomfrey at dawn. And McGonagall was quite insistent today – classes are to continue as usual, we are to be alert and keep our students safe, but not disrupt their schedules more than absolutely necessary," the Doctor said reluctantly. "So, let's see… my first break of any appreciable length on Monday is just after your section of Defense Against the Dark Arts. Shall we meet in the courtyard then?"

As much as John wanted to head straight to bed and sleep off the oddity of pleasantly wishing Professor Smith – the Doctor – a good night, he turned instead to the hospital wing, Sherlock and Lindsay following along. Madam Pomfrey was dozing beside Dennis Creevey's bed, but there were two more patients than there had been when they'd left. The knot in John stomach clenched.

Madam Pomfrey awoke as her wand vibrated on the bedside table. "Oh! John, you should be in bed."

He smiled. "I thought you'd need some help changing the dressings once more."

She didn't waste energy arguing. Sherlock went to check the potions Victor had left to mature, and the other three reapplied the paste to the wounds, quieted those whose potions had worn off and administered more. If only he wasn't so dog-tired, it would have felt nearly homey.

"Any word from St. Mungo's?" he asked as he finished wrapping Robert's bandage.

"They said they'll try to have someone here by 10, but they're trying to find healers who haven't been exposed to the spattergroit, because the last thing this school needs is an epidemic on top of everything." Madam Pomfrey sounded slightly bitter. "I'm in no position to argue with them."

John put a hand on her shoulder. "Half of this school would be dead but for you. Just you mind that."

She gave a huffing breath that might have been a laugh and regained a semblance of her usual snap. "And speaking of half-dead, I want the three of you in bed in the next 10 minutes or you'll all wind up in here yourselves. I'll send Peeves after you to check."

It seemed his head had barely touched the pillow when the commotion of the dormitories emptying for the morning woke him. John stumbled out of his room and made it to the Great Hall in time to grab a slice of toast before Transfiguration, where he embarrassed himself quite handily by forgetting the name of every magical theorist they were to have looked up over the weekend. Lindsay saved him from one last humiliation by actually interrupting Professor McGonagall's question to him to answer it herself. The mildly reproachful look McGonagall sent her told John she knew full well why Lindsay had done it. That fact only served to make him feel slightly worse.

His only recollection of Defense Against the Dark Arts was sitting down several minutes before class began and leaning over to put his book bag down. The next moment he was aware, Sherlock was sitting beside him, feet up on the desk, and the rest of the class was filing up to put their essays on the desk and leave.

John swore. "You mean I slept through the whole class."

"Quietly, if it makes you feel any better," Sherlock said, shrugging. "No snoring loud enough to disrupt anything. And you didn't miss much."

John rifled through his bag. "Our essay. We never finished our –"

Sherlock pulled a parchment from inside his robe. "I finished it during History of Magic this morning. Wasn't much left to do."

John stared at him as the last few students trickled out and Lindsay wound around several desks to get to them. Sherlock saw the look and frowned.

"Don't be grateful, it's annoying. I knew you'd never be able to focus on the hunt if you thought you had work left undone. You're too conscientious a student for that. So I removed the obstacle."

The Doctor walked up and took the parchment from him. "I look forward to reading this soon. But for now, who's up for a stroll in the woods?"


	16. Chapter 16

The Doctor turned on his heel to head back to his desk. "Just let me put this away and –"

"Doctor," Lindsay interrupted.

He paused, and Lindsay pointed her wand at the parchment. It struggled free of his hand and zoomed to his desk.

"Ah," the Doctor said with a short nod. "Right. Gotta get the hang of that. Blimey, that'd be handy."

"And we're off," Sherlock said, striding to the door before the Doctor had finished speaking. "I think we should start on the south side –"

He was interrupted in his turn by Professor Flitwick, who barely jumped to the side in time to avoid the collision in the doorway. He cast a disgruntled look up at Sherlock, but focused on the Doctor at once.

"Smith, the headmistress said to come fetch you. There's been another incident in the kitchens."

The Doctor blinked. "Right. I'll be right there." He looked at the trio of students before him, and back at Flitwick's impatient face before continuing, "You three go along now. It's too nice a day to waste inside."

He gave a slow wink as he passed them and mouthed _courtyard_, though his movements were so exaggerated that it took John a few seconds to be certain that was what he had actually said. They let the professors precede them into the hallway and Sherlock took the lead, keeping them just far enough back that they seemed to be out of earshot, but could still catch snatches.

" – can't have happened more than a few moments before I came to fetch you," Flitwick said, his voice rising in agitation. "Another one taken, just like that."

"Taken?" The Doctor repeated. "Not eaten there?"

"Precisely," Flitwick said. He cast a glance over his shoulder and lowered his voice so they couldn't hear his next words.

"Up the flue again?" The Doctor asked, not modulating his pitch in the slightest.

Flitwick shrugged and spoke again, though the only words John could make out were "assume," "vanished" and "elves didn't see."

Flitwick sped up his pace so even the Doctor had to lengthen his stride to keep up. Sherlock didn't do the same, allowing the adults to reach the stairs well ahead of them.

"Didn't take the flue," he muttered. "Why?"

"We just lost our chance to find out," John said, hurrying the last few paces to the top of the stairs and seeing the professors at the foot of the flight. "And do we know for sure it didn't?"

"Only logical reason for that combination of words, John. And Flitwick would have been suspicious if we'd kept pace. He knows I eavesdrop better than most."

"If it didn't take the flue, do you think it's still in the kitchen?" Lindsay asked.

Sherlock made a noncommittal noise. "A deviation from its pattern, another one. It's getting rather alarmingly erratic." He smiled suddenly. "Good news for us."

He'd turned and bounded down the steps before John could formulate the words, "How is it good for us?"

Lindsay clapped him on the shoulder. "C'mon. I'm sure he'll explain." She hopped onto the banister. "Whether he needs to or not."

She let go of the gargoyle at the landing and sped off down the slope. John chuckled, but took the stairs the old-fashioned way. The last time he'd taken the banister was one of the first DA excursions the year before, when the novelty of being out after curfew had yet to wear off. Perhaps it would have been advisable in this case, but he didn't like to associate that relatively carefree moment with this one.

The others were waiting for him when he hopped the last few steps, disagreeing already.

"I still say we could sneak in without them noticing," Lindsay said.

"It won't have stayed in the kitchen," Sherlock retorted. "And if it did, I rather think the dozens of house elves or perhaps the two professors going in search of it might catch a glimpse."

He was scanning the walls with his eyes already. "If we assume it didn't go out the flue and it's not still in the kitchens, what are our other options?"

"It could have come this way, like it did that first night you found the scratch marks," Lindsay suggested. "When the door opened to let them in, it could have sneaked past them. You said it has the ability to blend in with its surroundings."

"Or the Great Hall," John said, the words coming out almost before they'd registered as thought.

"What?" Sherlock asked, his voice sharp with interest.

"The Great Hall," John repeated. "How do you think they send all the food up? Remember, Lindsay? They've got the doors by each table so they can take care of messes and magic the food on and off the plates without people noticing." Sherlock was staring, so he pressed on. "We went through the kitchens several times last year for the DA. I know where the openings are. We can at least check."

Sherlock nodded and turned toward the double doors without further comment. The sight of the Slytherin boy leaning against the wall beside them pulled all three up short.

"Moriarty," Sherlock said, his voice somehow deeper. John thought he'd done something to his collar, too, making himself look a bit taller and more impressive than usual.

"Holmes." Moriarty's gaze slid over Lindsay and John. "Odd company you keep these days, even for you. I suppose when you get truly desperate –"

"Would you mind shutting up now?" John broke in. He could feel Lindsay and Sherlock both staring at him, but he found the boy as unnerving as he had two days previous and was in no mood to waste time on him. "We've got business to take care of, and you're keeping us from it."

Moriarty pushed off from the wall and walked up to John, smiling in that reptilian way that made John's skin crawl. He stopped mere inches from John's face and turned to grin at Sherlock. "I think I can see why you keep this one around. Good little watchdog, isn't he?"

John had just clenched his fist and was in the process of convincing himself not to drive it into Moriarty's jaw when Lindsay's wand came between their faces and settled with the end firmly against Moriarty's cheek.

"I think he said to shut up, and I quite agree with the sentiment," she said.

Jim chuckled. "A pair of them, then? Well, isn't that adorable?" Lindsay's wand pressed harder into his cheek, but he merely stepped back a half step and focused on Sherlock again, who was watching the proceedings with a bemused expression. "If you're up to what I think you are, you should just run along to your next class and forget about it."

"Really? Well, if the great Jim Moriarty has spoken –" Sherlock said sardonically. "What's the matter? Haven't covered your tracks as well as you ought this time?"

John furrowed his brow, trying to follow Sherlock's reasoning to how the Slytherin could possibly be involved with the alien, but Jim was laughing, and the sound made his skin crawl.

"I'm not the one who put those kids in the hospital wing," Jim said, his voice dripping creepy innocence. "I just think you ought to stay out of it. Consider it a friendly warning."

"Yes, well, thank you for your concern. Now leave," Sherlock said, opening the doors to the Great Hall and motioning to the Gryffindors to follow.

John unclenched his fist with physical effort and turned away from the smirking Slytherin. It took only another breath for Lindsay to lower her wand and follow suit. Whatever Moriarty's involvement or lack thereof, they had a creature on the loose and a trail growing colder by the moment.

The Great Hall was empty. John expected it to be so, but it still felt odd to be there alone in broad daylight. Sherlock's gaze went straight to the floor, keenly checking each flagstone for markings. John and Lindsay guided him along the tables, pointing out the moveable stones the house elves used.

"Aha!" Sherlock cried as they turned down the length of the Ravenclaw table.

A stone was slightly out of position halfway down the aisle. Sherlock dashed up to it, sliding into place beside it almost flat on the ground. He had his wand out, and was already following the miniscule markings he found as Lindsay and John caught up to him.

"Up, over the table," he muttered, moving from the horizontal position to standing, then onto the bench. "Over to the Slytherin table." He followed suit, hopping to the ground between the two tables and then onto the Slytherin bench. "And from here – up the wall, perhaps?"

John and Lindsay clambered over the Ravenclaw table and dashed around the end of Slytherin to catch up.

"Sherlock," Lindsay called, pointing to a spot several feet over on the floor. "Blood."

Sherlock vaulted forward to examine it. "Still fresh. Not left more than two minutes ago. So if it didn't come out the doors, and the windows are still intact, what does that tell us?"

A drop of blood fell from somewhere above and splashed on the stone beside the first. The trio looked up into the bright, near-cloudless enchanted ceiling. It was impossible to see if anything lurked beyond the blue barrier.

"It's still here."

John stowed his wand in his robe and turned to the wall. "Lindsay, cover me. Sherlock, keep your eyes peeled in case that thing bolts."

Lindsay grabbed his hood and held him back from the wall. "And why are you the one going up?"

"Because I want Sherlock's eyes down here where he'll have the best view of the hall and I want you down here where you're sure of a good shot when I flush it out." She was still frowning at him. He cocked his head at her stubbornly. "Don't make me pull rank.

It gained a smile, but Sherlock rolled his eyes. "She's a faster climber. You're a better shot. Lovejoy should go up and you should cover her."

"We don't know what we're facing up there," John protested staunchly.

"Of course we do – roughly," Sherlock said, shrugging. "Six-limbed bear-like creature with a stinger that delivers pain-inducing venom."

"And you think I should just let someone else face that?"

Lindsay had already edged around him and climbed several stones before he could get more than a garbled protest out. She grinned down at him. "Not your decision to make."

John tightened his jaw over several curses before settling on a simple, "Be careful."

Lindsay laughed. "If I don't, you owe me a dramatic rescue."

John did not reciprocate the laughter. "Not a favor I plan on repaying in kind."

Lindsay grinned and scrambled several feet higher. John pulled his wand back out almost savagely, feeling his body tighten into battle stance. Sherlock, by contrast, had relaxed to the point of limpness, hands sagging into his pockets and shoulders slumped. His eyes were scanning the ceiling with an intensity John could recognize, but the sigh he released made John's hackles rise.

"Bored?" he snapped.

"Yes, actually," Sherlock said, not breaking his scan of the ceiling. Lindsay had reached the blue sky and was climbing through it beyond their range of vision. "This isn't my idea of a rousing good time."

"Lovejoy, report!" John called anxiously, then wheeled to face Sherlock, spitting out the words in rapidfire rhythm. "So sorry chasing a bloody monster around isn't intellectually stimulating enough for you. Maybe it'll challenge you to some sort of Arithmancy duel when we catch up with it. Lovejoy!"

"No sign of it," came her voice. "Just rafters."

"I want reports every fi-"

John's instruction was cut off by a ragged cry from above and a brilliant red flash illuminated the ceiling. The blue disappeared, showing the matrix of rafters that hid above it, and the small figure of a Gryffindor clinging to a beam above the Ravenclaw table, wand pointed to her left. The light died, but there was a screech from above that certainly wasn't human.

"Got it!" Lindsay shouted down a split-second before a second bolt of red revealed a large creature scrabbling at the rafter just forward and left from Lindsay. The body of a house elf was clutched in one of its right limbs, and it was swiping angrily at her with both of its left. Lindsay swore and sent another Stunner at it.

"Don't muck about. Just use the Killing Curse!" John shouted, pointing his own wand even as the blue sky obstructed his view.

Sherlock aimed his wand at the spot the creature had been and muttered something under his breath. There was a jet of blue light, and the sound of a rafter cracking. A shouted spell that ricocheted off two walls above them. The creature was revealed scrambling onto another rafter from the one Sherlock had cracked. John spared a millisecond to marvel that Sherlock had pinpointed the correct rafter without being able to see it, then focused on Lindsay, whose third Stunner revealed she was backing away from the creature as quickly as possible.

"Just kill it!" John shouted. "Stunners aren't working!"

Another flash of light, this one purple, gave John a split second to aim. His Killing Curse blew into the radiant sky and smashed into the wood where the creature had been moments before. It was nowhere to be seen. The ceiling went blue again.

"Lindsay?" John shouted. "Where is it?"

"It's on the rafter with her," Sherlock said calmly, dashing down the aisle to be more directly under the fracas.

John swore. "Lovejoy, just jump!"  
She obliged, barely giving him time to cast _impervioscurrsus_ to break her fall. She righted herself in a moment, wand at the ready.

"Did it get you?" John asked, breaking his scan of the ceiling only long enough to ascertain there were no bleeding injuries.

"No, I never let it get close enough," Lindsay said, slightly breathless. "It's bigger than I expected."

The doors burst open and Flitwick, McGonagall, and the Doctor ran in.

"Where?" the Doctor shouted, immediately following their gazes up.

"Somewhere on the other side of the sky," John replied, trying his best not to think of how ridiculous that sounded.

Flitwick drew his wand and drew a complicated design in the air, muttering unintelligibly. The blue lifted, revealing the rafters above and the damage the students had already inflicted, but no creature. The professors instinctively spread out, Flitwick and the Doctor each heading to the corners of the room, while McGonagall moved forward down the center aisle. John nudged Sherlock and Lindsay and indicated that they should move to the forward corners, positioning himself on the same aisle as McGonagall. She had her wand raised and waved it in an impressive arc.

"Revelio!"


	17. Chapter 17

Nothing happened.

John saw a shadow of legitimate fear on Minerva McGonagall's face. He tightened his grip on his wand and scanned the ceiling yet again, looking for a shadow. Anything.

"There!" shouted Flitwick, waving his wand toward the rafters above the door.

The jet of red light struck a solid body where John had seen nothing. The creature turned a deep blue, revealing itself hulking with its back to them. A veritable rainbow of spells shot toward it, but it leapt onto the wall, evading them all and dropping the house elf to the floor. The ravaged body fell with a soft, sickening splat, and the creature scrambled to the left to avoid the yellow light from McGonagall.

"It is a Zhacan!" The Doctor exclaimed, running forward and squinting at it. He pointed the sonic screwdriver and pressed a button.

The creature let out a roar and scrambled down the wall to the open door. John pointed his wand at the doors, but spells flew from almost every corner. The doors slammed shut just as the creature's tail disappeared through them.

"C'mon," the Doctor shouted. "And don't aim to kill."

"It's tried to murder six students!" McGonagall shouted back as she magicked the doors back open. "The time for clemency is past."

"Zhacan are peaceful creatures. Something must be wrong with it"

The Doctor dashed out into the entrance hall, where a slightly stunned Jim Moriarty was picking himself up off the floor.

"Did it touch you? Did it sting you?" McGonagall asked, pulling him roughly to his feet.

Moriarty shook his head.

"Which way did it go?" the Doctor asked, spinning in a near-complete circle.

John kept his eyes on Moriarty, searching for the slightest hint of deception. The boy's eyes were wide, but there was a control in the terror depicted on his face that John did not like.

"I didn't see. It vanished. Right in front of me."

The Doctor nodded. "Right. So we split up. Minerva, Filius, pick a direction and a student to take along."

Sherlock held up a hand to stave off McGonagall's protests. "We know which way it went."

The Doctor studied Sherlock's face for several long seconds. "Okay. You lead."

"The children shouldn't come," Flitwick spluttered.

"We've been involved right along, sir," John said, his voice edged with the same steel he'd known last May when he and Neville had gone toe-to-toe with McGonagall to be allowed to stay and fight. "You'll need us."

"Filius, Minerva – you should stay here to keep the other children safe," the Doctor said, a note of finality in his voice. "I'll take these three. They know what they're about. We'll go after the Zhacan."

McGonagall was livid. "I will not allow you to put more students in danger."

"You're doing that right now," Sherlock said impatiently. "We know which way it went and probably where it was going. You're slowing us up. We'll have to catch up to it. If it gets away, we'll have lost our best shot at stopping it."

Flitwick and McGonagall both looked so torn that John almost pitied them. The Doctor nodded at Sherlock, who took off toward the front doors, Lindsay at his heels.

"You two stay here in case it doubles back," the Doctor told the professors. "Keep everyone inside. We'll be back."

John spared one look for Jim, who wore the same gleeful expression he'd seen on Sherlock's face when he was putting information together. But the Slytherin made no move to follow them as he and the Doctor pounded out the door after Sherlock and Lindsay.

The alien was nowhere to be seen, but Sherlock was already tracking across the yard, bent almost double to examine the grass.

"It came this way," he called back, motioning them forward without taking his eyes off the ground. "The weekend rains left the ground just soft enough for those claws to leave marks."

John didn't see anything other than grass that had been walked on by dozens of students over the weekend, but there was no point in saying so. They were following a fairly direct line toward the Forbidden Forest, angling away from Hagrid's cabin and toward the lake. Sherlock's self-assured pace faltered only once after they'd entered the forest and the markings became less distinct.

"It knew exactly where it was heading," he said as his half-run slowed to a walk. "The markings are almost gone, but we should keep to this line." He turned to look at the Doctor.

"You said you recognized it as a Zhacan – anything that can help us?"

"They hate high-pitched noises," the Doctor said, raising his sonic screwdriver.

There was a roar from the direction of the lake, just over the rise of land.

"Well, that got its attention," the Doctor said. "Alright, we're going to have to try and surround it. Zhacan like nests near water, so I bet it's got itself a nice little hideaway over there. If it feels outnumbered, it might go peaceably."

"Go peaceably where?" John asked, crossing his arms.

"If it is willing to leave this place, I can take it in the TARDIS to its home planet – or some other planet. Something made it attack people and I don't understand what it could be. They avoid humans. They're not aggressive creatures as a rule."

The Doctor retreated into a brown study. Sherlock waited about two breaths before breaking it.

"So should we go after it or let it hide itself even better than it already has?"

The Doctor shook himself. "I'll take one of you and go north, and the others can go around to the southeast. We'll try to keep its back to the water. If it's really a Zhacan, its invisibility should last only about 3 minutes at a time, and agitation causes it to lose the pigmentation. If it gets too close, just whistle as loud as you can or make some sort of high-pitched noise."

He looked the three of them over. "I'll take Lovejoy with me."

John couldn't help but wonder if the choice was because he actually wanted Lindsay with him, or because any of the other pairings seemed untenable. He gave Lindsay a salute and turned to head off with Sherlock.

They didn't speak as they made their way around the rise toward the lake, communicating with hand motions and jerks of the head. Sherlock's eyes were only half-focused, which could only mean he was thinking of something else. John tried not to worry too much about having Sherlock's attention divided – it stood to reason that half of Sherlock Holmes' attention would be at least as good as the average person's full attention. He had to chuckle at himself – had it really been a week ago that he'd been dreading spending more than five seconds in the Ravenclaw's company? The boy had surprised him.

"We're missing something," Sherlock muttered, following John's lead to crouch behind some brush where the rise leveled out.

John motioned him silent, peering around the branches to the lake. There was a stretch of shore that was well trampled and a depression in the side of the hill that couldn't quite be called a cave but seemed to be deep enough to hide the creature. A flash of movement caught his eye. The Doctor and Lindsay were diagonal from them, closer to the edge of the lake, taking up positions behind two large trees. Sherlock had closed his eyes and furrowed his brow, lips moving in silent monologue.

"Sherlock!" John hissed, elbowing him. Sherlock's eyes opened, and he glared at John. "This isn't the time!"

"Very well, then, I suppose it would be better to face down the killer alien without considering all the information."

John didn't bother responding. The Doctor waved once to get their attention, then motioned toward the cave, pointing toward himself. He drew a circle in the air, and motioned to the three students. John gave a firm nod. It had nothing to do with letting the adult take the risk and everything to do with putting the wand-wielders in a position to protect the one who know enough to dare to get close. Besides, he wasn't certain he could classify the Doctor as an adult.

"Get ready," he muttered.

Sherlock obliged insofar as he drew his wand and assumed a position that allowed for greater movement, and his eyes dropped a fraction of their distracted expression. John set himself up with a direct line of sight to the alcove and readied his wand. The Doctor stepped out from behind the tree and took several experimental steps into the open.

"Anybody home?" he called. "We're not going to attack, we just want to see you."  
John didn't like the idea of that particular promise. Whatever the Doctor said about the Zhacan being peaceful, he wasn't above aiming to kill the creature.

There was no response. The Doctor took a few more steps. John let his eyes relax, focusing on detecting movement rather than details. The Doctor's slightly-swinging arms and the light breeze from the lake rustling a few leaves were the only things moving.

"Come on, then, it's rude not to acknowledge guests," the Doctor called, raising his sonic screwdriver. "I don't want to have to use this."

A sudden bank of blue to the left. John swiveled half-around the bush and trained his wand on the Zhacan that had materialized in the mouth of the cave. For a moment, the clear view of the creature froze him.

Winky had been right – the alien had bulbous red eyes that looked like those of a fly. The dark blue fur appeared short, which meant the mass of the limbs and torso had to be mostly muscle. It moved from a crouching position to stand upright, well above the height of a man, and swished its tail to curl around in front of its feet in a casually threatening way. John Watson did not consider himself a fearful person, but the sight of it had him thinking nostalgically of facing Death Eaters and acromantulas.

The Doctor seemed unperturbed. "Hello, there!" he said, smiling cheerfully. "Now, we're got to have a talk about your choice of home."

The Zhacan let forth a roar.

"Yes, I know, you came here in search of food. No one can blame you for settling where there was a ready supply. But you can't stay." The Doctor put his hands in his pockets and looked for the world as if he was reasoning with a petulant child. "You've done harm here. I won't allow it to continue."

The Zhacan made another noise, less ferocious and more questioning.

"You crossed the line. You attacked innocent humans. Children. Do you understand?" The Doctor said, his tone hard.

This time, even John could recognize that the sound the Zhacan made was meant to convey confusion.

"Don't play dumb. You know exactly what I'm talking about."

The Zhacan bared its teeth and lashed out. John didn't wait for the Doctor's reaction. He aimed and fired off a stinging jinx at the alien's chest.

The Doctor's horrified yell was secondary to John's concern that he be alive to make it. The creature stumbled back, and roared again, but immediately charged forward at the source of the spell. Sherlock flicked his wand and several roots came up to tangle around the alien's feet. It fell in a mass of limbs and claws, and scrambled to its feet again before John could draw breath.

"Calm down, all of you!" the Doctor shouted, fiddling rather desperately with his sonic screwdriver.

Movement to his right caught John's attention. Lindsay had dashed forward and shot a brilliantly blue spell at the creature. It landed under its second set of arms and set the whole creature into a rather grotesquely violent form of a dance. It careened away from John and Sherlock and back toward the water.

John took a moment to appreciate the fact that Lindsay had actually found a use for tarantallegra, which had always seemed a rather pointless jinx, but the creature seemed to have shaken the spell off almost at once. Lindsay backed away toward the cave, wand raised. The Zhacan let out its strongest roar yet and charged. The length of its stride was impressive. And terrifying.

John looked to his left to coordinate with Sherlock, only to find him gone. John swore. The Ravenclaw was halfway to the cave himself, attention caught by something John couldn't see. The Doctor was moving forward, eyes still on the implement in his hand.

"Don't cast any more spells. We can settle this peacefully!" he said, pressing a button the screwdriver.

Nothing happened.

The creature had drawn up at the sight. The split-second hesitation was the only diversion John was likely to get. He made his decision.

Lindsay was standing with wand raised, a look of indecision on her face. Sherlock had reached the mouth of the cave and was peering in. The Doctor was waving the sonic screwdriver around like a mobile phone trying to get a signal. In another two seconds, one of them would be cut to ribbons on those long claws.

John took three long strides and dove around the Zhacan, flinging himself down on his back in front of the Doctor and Lindsay.

"Protego!"

The shield charm that ballooned out from his wand knocked the Zhacan onto its haunches. John ignored the jarring his shoulder had received and held his wand steady, keeping the transparent barrier between them and the creature.

If it had a recognizable expression, John would have called it rage. The creature was positively mad, swinging all four of its limbs at the shield, which so far was holding up better than the rest of their spells.

"Good thought," the Doctor said, smiling. "I told you the screwdriver has been on the fritz. Apparently its only up for a couple of uses a day around here. Well," he said, smiling through the barrier at the Zhacan. "This is a nice way to settle things. Tell me, are you full Zhacan?"

John didn't need the Doctor to translate the sound the Zhacan made. It had no intention of answering any of their questions.

"You look the same. Exactly the same. I find it hard to believe that a mutation that powerful wouldn't have affected your form in some way. C'mon, you can tell me."

"Whatever else it is, I believe I know why it's been taking house elves rather than eating them in the castle," Sherlock said from behind them.

He sounded so matter-of-fact, John had to wonder if he realized they were facing down a killer animal and not discussing theory in potions. Then he heard Lindsay's surprised exclamation from behind, and saw the Doctor's whole body sag in surprise. He risked turning his head slightly to see what had caused such a reaction.

Sherlock was crouching at the mouth of the cave, shining his wandlight inside. Two pairs of bulbous red eyes stared at the humans in frank confusion.

"What the –" John hesitated to find the correct expletive.

"It's a mother," the Doctor said.


	18. Chapter 18

The Zhacan roared at them from the other side of the shield charm. John returned his full attention to maintaining its strength, edging himself into a sitting position.

"Alright, then," the Doctor said, walking back to the edge of the shield. "So you've been stealing for your children. Forgiveable. Commendable, even. But that doesn't explain the attacks on the students."

The animal shook its head. The sounds were a bit more pleading, less ferocious, but carrying an unmistakably defensive growl.

"Now don't change the subject –" The Doctor said warningly.

The Zhacan growled again. The Doctor spun on his heel and headed back to the cave.

"This one?" He asked, pointing at the larger of the two cubs.

The creature nodded.

He reached out to it slowly, offering his hand as if to a dog. "There now, I'm not going to hurt you. I just want to have a look. Mummy says it's okay."

Both cubs seemed to vanish. The Doctor sighed. "There's no need for that. We're here to help."

He warily put his hand out further. Lindsay and Sherlock had their wands out on either side, poised for the first sign aggression. John alternated his attention between the scene unfolding behind him and the alien pacing on the other side of his shield charm.

"Come on, you can trust me," the Doctor said, apparently having made contact with the alien's fur. He petted it experimentally. "I'm the Doctor, I'm going to fix it."

The aliens slowly faded back into a blue. The smaller cub was looking at the Doctor with an expression of utter terror, the larger seemed to be relaxing into the caress.

"Alright, then. Mummy says you've got yourself hurt." The Doctor eased the creature into a reclining position and nudged its curled limbs away from its abdomen. John stopped swiveling his head to stare at the long, bloody slice across the cub's stomach and down its left side.

The Doctor hissed in a breath in sympathy. "That's got to hurt a bit. What happened? Try to take down a centaur on your own?"

The cub mewed, but even John could discern the hint of pride in the sound.

"Oh, the thestrals. Aren't you the adventurous one?" The Doctor said. He glanced around at the students around him. "A bit stupid, but adventurous, I grant you. Must be in the air around here."

"You're one to talk," Lindsay muttered.

John laughed. Sherlock let out a sound that could have been a snort or a laugh, it was difficult to tell. The Doctor smoothed the fur back from the injury, shushing the little pained sounds coming from the cub. The mother stopped her pacing and was standing, paws drawn together in concern, watching the Doctor's movements. John braced his elbow against his knee, resting his wand arm for a moment.

There was a screeching snarl from the cub. John's head whipped around in time to see it clawing away from the Doctor's reaching hand. He pulled back, but the smaller cub had gathered itself, hackles raised, and struck with its tail.

The mother Zhacan threw herself against the shield yet again. With John's attention divided, it crashed through the charm, roaring. John scrambled to his feet and backed up, but it was Lindsay's shouted "Protego!" that brought another shield up.

"Thanks," John muttered.

Lindsay nodded, keeping her eyes on the Zhacan. John hurried over to the Doctor, who had fallen over on his side. Sherlock had pulled his sleeve up and was examining the puncture wound.

"How do you feel?" John asked.

"A bit… woozy," the Doctor said, his voice thick.

John leaned over his arm, edging Sherlock aside with his shoulder. "Pain?" The puncture was about the size of a wand tip, but had torn the skin around the wound, creating a slight claw mark across his wrist.

"Not that I can tell," the Doctor said.

"Well, the others didn't experience any pain at first, either."

"Don't be thick, John, it's not the same wound," Sherlock said sharply.

"It's possible the younger ones' venom reacts differently," John said, continuing his examination of the wound.

Sherlock's voice sped up. "The others' marks were completely smooth. Completely. This one has jagged edges. There's no way it could have been made by the same implement. And the students didn't feel a thing when the wound happened. The Doctor, on the other hand, is clearly experiencing the effects of a muscle paralytic. Exactly like what he told us a Zhacan's stinger is supposed to deliver. Lex parsimoniae - we've got two villains in this story. Well, now, that makes it all a bit more interesting, doesn't it?"

"Yeah, a bit," John said, quickly checking the Doctor for any signs that this was anything other than what it appeared.

The Doctor was already pushing himself into a sitting position – his movements slow and jerky, but functional. He pointed to the cub. "Check him out. See if you can do anything about that wound."

John turned warily to the creature, who was staring at him with equal distrust. He held out his hand for it to sniff, which it did with a hint of curiosity. He reached for the wound. It recoiled, showing an impressive set of teeth. Its younger sibling growled.

John withdrew his hand, looking to the Doctor for guidance. The Doctor nodded at him with an effort.

"Just talk to it. It will understand."

"Right," John muttered under his breath as he extended his hand again. "I'll just talk to the cute little alien and hope it doesn't try to bite my fingers off."

"It can hear you, John," said Sherlock, who had trained his wand on the creatures. "Perhaps a bit more diplomacy."

"That's rich," John said, smiling. He made eye contact with the cub. "You don't know how funny that is, but believe me, it's a laugh. Now, I'm going to take a look and see if I can fix this for you. I'll do my best not to hurt you. I promise."

The cub relaxed its limbs and let him see the wound. The spell was a familiar one, but he'd never before performed it on a creature he half-expected to attack his wand. John waved it slowly, repeating the incantation over inch-long segments of the cut. From behind him, he could hear the mother paced and huffing, growling deep in her chest.

"Any chance of speeding that up?" Lindsay called, a laugh in her voice that John wasn't sure was genuine.

"Steady on, John," the Doctor said, smiling encouragingly. It was a bit lopsided, but the thought was clear. "But – as quickly as you can, eh?"

"Anybody else want to volunteer to do it faster?" John demanded.

The other three exchanged glances, but said nothing. John turned his attention to the final segment. The relief that came when it closed up and the skin turned blue like the rest of the creature seemed disproportionate to the act, but he didn't question it.

"There now," he said, releasing the breath he'd been holding for longer than he realized. "You're all sorted. You'll be up chasing creatures you shouldn't in no time."

The cub moved experimentally, then curled into a ball, then leapt up against John, knocking him back on his haunches like a large dog. A shock of something – either surprise or fear – ran through his limbs, but he held himself steady as the claws landed on his shoulders. They did not sink through the fabric, and the expression in the alien's eyes was questioning as it leaned closer to his face.

John could feel Sherlock and the Doctor moving closer. He made the slightest shooing motion with his hand, keeping eye contact with the cub, who was leaning closer until its snout was angled against his chin and its eyes were about two inches from his. The smaller one was edging closer, too, reaching out with one paw.

"Lindsay," the Doctor said, moving with greater fluidity as he rose to his feet and turned toward her. "Go ahead and let the shield charm down."

"What?" The question came from both Lindsay and Sherlock, who looked as if the slightest sound might send him into a frenzy.

"She wants to be with her cubs," the Doctor said. "And she'll be able to control them."

From the corner of his eye, John saw the Doctor walking up to the mother. "Your cubs are alright now. I'm going to let you come to them. But you have to promise me you will leave this place immediately."

The Zhacan gave a ragged sound that John hoped was agreement, because Lindsay let the shield charm down. The mother alien didn't waste any time in reaching her cubs. John kept his position, still keeping eye contact with the inquisitive cub, but expecting –

A heavy paw crashed into his left shoulder, knocking him to the side. There was no claw, but the weight of the blow sent him all the way to the ground, flat on his back. Sherlock scrambled to his side. "Did it hurt you?" he asked, running his eyes over John.

"No, I'm fine," John said, pushing himself into a sitting position.

The Zhacan had cradled both of its young into its lower set of arms. Its upper arms were out defensively, and the expression on its face did not bode well.

"I can take you back to Zhactarm today," the Doctor said. "Are there more of you?"

The Zhacan shook its head, mewing.

"You don't want to go back? Whyever not?"

Another growling roar from the Zhacan, longer, as if it was telling a story.

Lindsay took the opportunity to join the boys. "So this thing didn't poison the students?"

Sherlock shook his head. "It was something else. _Someone_ else. Someone in the castle. It has to be. But who?"

The Doctor laughed. "You had a fight with your mum-in-law and stormed off with the kids and he didn't follow you? Honestly? Worse than humans, you are."

The Zhacan gave a disgruntled snort.

"Well, I'm sorry this is such an inconvenience for you, but you're not staying on this planet. And I think you ought to go home and make things right. Family is important, you know."

The Zhacan appeared to consider this. John brushed the dirt from his robes and looked over at Sherlock.

"It would have to be a very gifted witch or wizard," Sherlock muttered. "You said you, Madam Pomfrey and Professor Slughorn together couldn't identify the poison. That suggests an adult, or someone with very advanced powers."

"Someone like you?" John teased, then caught himself, an idea forming behind the joke. "Someone like Jim Moriarty?"

Sherlock's eyes narrowed. "Possibly. Though it's a bit ostentatious for his style."

The Zhacan snorted suddenly, shaking its head.

"Come on, now," the Doctor said chidingly. "Don't be like that. I'm sure he misses you."

Another snort.

"Alright, so he should have come after you. But he didn't, and you could go on being mad at him and planet hopping forever, or you could take your kids and go home – let them grow up in a proper nest with lots of friends and no strange creatures coming after them night and day. Or you can choose some other planet at random and hope for the best. I just think my way seems easier."

Sherlock was frowning in concentration. "Someone who could create something like that –"

"And has access to students from all four houses a different points during the day," John said. "The poison was delayed, remember? We had people coming into the hospital wing over more than 12 hours. Not someone too impatient, I suppose."

"And Victor said the poison had traces of the samples from the Zhacan. So someone who knew about the –" Sherlock broke off, eyes sliding out of focus, mouth going slack.

"What? What is it?" John asked.

Sherlock turned on his heel and started running back toward the castle. "I know who the poisoner is!"


	19. Chapter 19

Sherlock waited until John and Lindsay had caught up to him before pushing open the potions laboratory door. John sucked in a deep breath through his nose and willed himself not to pant after their sprint from the lake. He hadn't seen Sherlock cast a spell, but he must have done, as the heavy old door swung inward in complete silence, unleashing the scents and sounds of several cauldrons bubbling within. No one was immediately in view.  
Sherlock slid his wand from his sleeve into his hand and stepped into the room, every line of his body in a coil. John was only a half step behind, wand already out and pointed ahead, Lindsay at his shoulder. The laboratory was empty.

Sherlock lowered his wand and dashed to the closest cauldron. He peered inside for a moment, then began rummaging amongst the ingredients strewn across two tables.

"Nettles, lovage, chomping cabbage – these explain the burning sensations, John."

"And why the burning bitterroot helped soothe it," John said, leaning closer, attention still partially on the door, to examine the table. "And I wondered if bulbadox mightn't be in there, too."

He was puzzled. So far, the ingredients were fairly innocuous – unpleasant, to be sure, but hardly adding up to the kind of suffering he had seen. There were lionfish spines and belladonna and runespoor eggs as well, all only slightly more dangerous. Overall, it looked more like some sort of stew than a sophisticated potion.

"Here." Sherlock said, picking up a small vial and holding it up to the light.

The liquid inside was the palest blue and milky-looking, but shot through with spirals of a darker, more translucent shade.

"Is that…" Lindsay took a few steps closer.

"A Exaggeration Elixir, yeah," John said, taking the bottle from Sherlock, who allowed it with only a passing frown. "It would take whatever is in there and magnify the effects. And the duration of the symptoms. Madam Pomfrey keeps some of this around in case of dragon pox – that way a little potion can be spread around to all the students. I wonder if this is from her cupboards. It's a controlled substance, have to be over 17 to buy it. And it doesn't come cheap."

Lindsay returned her eyes to the door, keeping her wand partially raised. "Anything lethal mixed in?"

John was still examining the ingredients, but Sherlock answered. "No, not even anything that could be lethal in larger doses. Someone was thorough."

"But why didn't Scarpin's Revealer spell work?" John asked, bending over the ingredients once more. "Hang on, here's an empty bag. Sherlock, any idea what was in this?"

He had just raised his head when a shift from Lindsay indicated they were no longer alone. His wand was in dueling position before he recognized the figure in the doorway.

"It's leopard's bane, relative of wolf's bane, most commonly found in Afghanistan. Professor Sprout just started growing it this year," said Victor Trevor, walking into the room with a casual calm that seemed to ignore the fact he had two wands trained on him. "The mashed leaves are a binding agent that will hold against all but the most powerful spells. Quite useful, really. I can think of dozens of applications."

John glanced at Sherlock, expecting a witty retort, but instead found him staring at Victor with – was that betrayal in his eyes? It wasn't an emotion he expected from Sherlock, but the 15-year-old seemed genuinely confused.

"So I take it one of those applications was poisoning everyone at Hogwarts?" John asked.

"Oh, not everyone," said Victor, smiling almost condescendingly. "Just the ones who helped land my uncle in Azkaban. And poison is such a strong word. I've given them a dose of a potion. It's not lethal. I made sure."

"Your uncle landed himself in Azkaban," John snapped.

Victor's face flushed. "He didn't have a choice! It was join up or get all of us killed. Voldemort knew he was one of the best spell creators in the country. Uncle Roget did what he had to do, and he got sent to prison for it."

They needed to block his exit. John made eye contact with Lindsay, was already moving carefully toward the door, keeping herself in Victor's periphery.

"But –" Sherlock had found his voice again, strained and unnatural, but functioning. "Consider the alternative. You would rather the rest of those men were still at liberty?"

"I would rather have my uncle back with his family," Victor snapped.

"That's not logical," Sherlock said, stepping closer to the Ravenclaw, a hint of accusation in his voice. "You always said too many people make the mistake of letting emotion keep them from the bigger picture."

Victor shrugged. "And I guess I'm one of them. Sorry, Sherlock. Here's another life lesson for you: people never live up to the morals they mouth."

"What was your plan? Poison all the DA members? Didn't you think people would make the connection? What was next? Get to McGonagall? Get to Potter, somehow?" Sherlock asked. "This was hardly thought out, was it?"

Victor's chin jutted out. "I didn't care if people made the connection. I wanted people to understand that being the winner doesn't mean escaping unscathed."

"Oh, we learned that lesson without your help, thank you," John said.

Victor curled his lip at him, but it was Sherlock who spoke, his voice still strangely subdued. "You know we're going to have to tell them, Victor. What does this mean for you? Expulsion?" A crack of heat was in his voice as he moved forward. "Perhaps a stint in Azkaban yourself? You didn't even bother to consider repercussions, did you? Didn't think that anyone in this school was clever enough to get to the truth."

"I'd expected to get farther along, possibly have more bargaining leverage," said Victor, returning to his cool, collected tone. "But really, does it matter? Two of you were on my hit list, regardless."

John instinctively ducked when Sherlock did, letting Victor's spell sail above his head and crash into a shelf. A jar of pufferfish eyes exploded.

Lindsay shot a spell from behind Victor, but he pivoted to the right and avoided it. John aimed around all three of them and magicked the door closed. Victor rolled his eyes.

"Oh dear, I'm trapped," he said mockingly. "There's no way I can ever leave this room. Mudblood fool."

Lindsay aimed a Stunner at him so powerful John could hear the air crackle around it as it crashed into the stone wall. Victor shot a spell in return, which Lindsay ducked. John took a moment to look around. Sherlock was shuffling toward the cauldrons on his knees while Victor was engaged with Lindsay. Lindsay and Victor were exchanging and parrying spells at lightning speed. Victor fought with the trained grace and rhythm of a duelist, keeping his body turned so he could turn at any moment to face an opponent from behind. John scrambled forward to cover Sherlock's progress and sent a stinging jinx at Victor. It ruffled his robe, but did not hit him.

Annoyed, Victor slashed a spell over his shoulder and turned to block one from Lindsay. John ducked and threw another Stunner. A shield charm rebounded it toward him, but it careened into the table instead, making the cauldrons wobble. The bolts of light dazzled his eyes as the duel continued. Victor was holding his own, blocking and retaliating with a panache John could almost envy. And his own skill was returning. He'd managed to slip two spells past Victor's guard, causing the unsightly swelling on the left side of Victor's face, and a dust cloud that had given John the split second he needed to get close enough to get into clear space. He was aiming to simply tackle the Ravenclaw, but the boy Vanished the dust and turned a particularly strong spell onto John, which he dove to the right to avoid.

"Stop."

It was Sherlock's voice, deeper than usual and positively intimidating in its authoritative chill. He was standing by the cauldrons, his wand tip dripping. Something flickered across Victor's fierce expression.

"Sherlock –" he said warningly.

"You think I couldn't figure out how the system works?" The boy smirked. "You shoot a stabbing jinx of some sort with the wand tip dipped in the substance. It creates a hole like a creature's stinger, and the potion is cleanly administered. Excellent idea. The problem with this type of administration, though, is that anyone could do it."

He flicked his wand and sent a spell whizzing directly between Lindsay and Victor. They both jumped a bit to the side.

"Now listen, Victor," Sherlock continued, dipping his wand back into the cauldron and glancing with some interest at the smoking divot in the wall. "There's nothing I can do to keep you from whatever punishment the Wizengamot decides on. I might be able to help your uncle, though, if you'll put down your wand and go quietly."

"Your negotiating skills need some work, Holmes," Victor said, grinning suddenly. "You're better suited to the world of theories." He flicked his wand to his left and a rope twined around Lindsay's torso.

Victor tugged it toward himself, positioning Lindsay as a shield between himself and Sherlock, over her squirming protests. John caught Lindsay's eye for a split-second, and she nodded. John made a low tackle that caught Victor's knees and threw all three of them to the ground. A swift punch to the jaw drove Victor's head back and into the stone floor with a rather sickening crack. His grip on his wand slackened for a moment, and John pulled it out of his hand. The boy reared up, and brought his knee into John's stomach. The air rushed out of his lungs painfully, and he crumpled. Victor shoved him aside, scrambling for his wand. John gathered himself with one gulp of air, and Victor's face collided with his fist. This time he relaxed onto the stone floor, apparently out cold.

John reached for his own wand and severed the cord holding Lindsay. He staggered to his feet and held out a hand to her.

"How's that for a dramatic rescue?"

* * *

The larger Zhacan cub seemed to be developing quite an attachment to him. John held it under his robes cautiously, as he maneuvered the corridors to the Transfiguration study. It snuggled closer to his cardigan and released a noise John assumed was the equivalent of purring.

"You'll have friends of your own kind soon," he told it.

The Doctor had convinced the Zhacan to leave with him, but for extra insurance, the cubs were coming to the TARDIS via John and Lindsay. Sherlock had no further interest in the creatures now that the mystery was solved, and had stayed in the castle to discuss Victor's situation with Professor McGonagall after they'd delivered the potion components to Madam Pomfrey. He'd agreed to meet them in the study when he was done to see the Doctor off, John assumed because he was curious to see how the spaceship was to take off or land from within the study.

"It's almost a shame they can't stay," Lindsay said, tickling the smaller one under the chin as they approached the door, where the Doctor was waiting. "They'd make great pets."

"Yeah, except for the fact no other animal would be safe around them," John said incredulously. "I don't want a pet that can almost take down a thestral."

"Alright," the Doctor said, rubbing his hands together. "Mummy's going to be joining us through the window. In fact, she's probably hanging around outside now. So let's get this done."

He opened the circular lock and rearranged the various curves and circles until there was an audible click and the door swung open. John let the little Zhacan down and herded it into the room on foot. The Doctor was already unlocking the TARDIS.

"I thought you said the TARDIS wasn't working properly," Lindsay said. "Are you sure you'll be able to make it back?"

The Doctor grinned. "Oh, I gave my word, never fear. I told Professor McGonagall she may need to cover classes for me for a few days, just in case I'm not as precise about getting back as I'd like to be."

"What if you waited till the weekend?" Lindsay suggested. "Then you'd have a buffer."

"I think you're trying to ask another question in all this, Miss Lovejoy," the Doctor said, smiling.

"She's trying to say that she'd love a ride in your space-traveling phonebox," Sherlock said from the doorway.

"And hello to you, to," John said by way of a remonstrance.

"I'm sorry, Lindsay, but I couldn't risk you missing your classes. What would your parents say?"

"That it's a valuable opportunity?" Lindsay suggested hopefully. "No, who am I kidding? They'd be horrified."

"Precisely. And you're not quite of age yet to make the decision on your own."

"Only a few more days."

"I'm sorry," the Doctor said firmly, leaning out to open the window. "Maybe at the end of term. Like an end-of-school road trip."

"Really?" Lindsay asked, eyes shining. John found himself almost jealous.

"Sure, if you want to come. Any of you," the Doctor said, his eyes lingering reluctantly on Sherlock. "It's the least I can do for you keeping my secret from the rest of the school."

The Zhacan climbed in through the window, eyeing all of them with distrust. The Doctor motioned it into the TARDIS door and shooed the cubs along with it.

"Well, I guess I'd better get going. With any luck, I'll be back from Zhactarm by tea time. If not, I'll be seeing you soon."

He gave Lindsay a hug, shook hands with John, and offered one to Sherlock with a rather uncertain air. The Ravenclaw took it briefly.

"You're legitimately mad," he said. "I hope you know that."

"Oh, I should hope so. All the best people are. Even you, I fancy," the Doctor responded.

He leapt into the TARDIS with one final wave and closed the door. The rusty sound John had triggered the other night came again, and the light atop the box began glowing. The phonebox was literally fading away, something John thought ruefully shouldn't be surprising after 7 years at Hogwarts. A glance at Lindsay's face, though, made him pause. She looked rather desperately disappointed.

The noise stopped. The box rematerialized. John exchanged glances with Sherlock and Lindsay, but neither face held any answers. The door swung open and the Doctor poked his head out.

"Or, maybe, just one adventure now?"

**Fin.**

* * *

To all my readers, thank you for following along. This story has been such fun to write!


End file.
